| Title: | Quantile Regression Neural Network |
|---|---|
| Description: | Fit quantile regression neural network models with optional left censoring, partial monotonicity constraints, generalized additive model constraints, and the ability to fit multiple non-crossing quantile functions following Cannon (2011) <doi:10.1016/j.cageo.2010.07.005> and Cannon (2018) <doi:10.1007/s00477-018-1573-6>. |
| Authors: | Alex J. Cannon [aut, cre]
|
| Maintainer: | Alex J. Cannon <[email protected]> |
| License: | GPL-2 |
| Version: | 2.1.1 |
| Built: | 2024-11-01 11:26:58 UTC |
| Source: | CRAN |
This package implements the quantile regression neural network (QRNN)
(Taylor, 2000; Cannon, 2011; Cannon, 2018), which is a flexible nonlinear form
of quantile regression. While low level modelling functions are available, it is
recommended that the mcqrnn.fit and mcqrnn.predict
wrappers be used for most applications. More information is provided below.
The goal of quantile regression is to estimate conditional quantiles of a response variable that depend on covariates in some form of regression equation. The QRNN adopts the multi-layer perceptron neural network architecture. The implementation follows from previous work on the estimation of censored regression quantiles, thus allowing predictions for mixed discrete-continuous variables like precipitation (Friederichs and Hense, 2007). A differentiable approximation to the quantile regression cost function is adopted so that a simplified form of the finite smoothing algorithm (Chen, 2007) can be used to estimate model parameters. This approximation can also be used to force the model to solve a standard least squares regression problem or an expectile regression problem (Cannon, 2018). Weight penalty regularization can be added to help avoid overfitting, and ensemble models with bootstrap aggregation are also provided.
An optional monotone constraint can be invoked, which guarantees monotonic
non-decreasing behaviour of model outputs with respect to specified covariates
(Zhang, 1999). The input-hidden layer weight matrix can also be constrained
so that model relationships are strictly additive (see gam.style;
Cannon, 2018). Borrowing strength by using a composite model for multiple
regression quantiles (Zou et al., 2008; Xu et al., 2017) is also possible
(see composite.stack). Weights can be applied to individual cases
(Jiang et al., 2012).
Applying the monotone constraint in combination with the composite model allows
one to simultaneously estimate multiple non-crossing quantiles (Cannon, 2018);
the resulting monotone composite QRNN (MCQRNN) is provided by the
mcqrnn.fit and mcqrnn.predict wrapper functions.
Examples for qrnn.fit and qrnn2.fit show how the
same functionality can be achieved using the low level
composite.stack and fitting functions.
QRNN models with a single layer of hidden nodes can be fitted using the
qrnn.fit function. Predictions from a fitted model are made using
the qrnn.predict function. The function gam.style
can be used to visualize and investigate fitted covariate/response relationships
from qrnn.fit (Plate et al., 2000). Note: a single hidden layer
is usually sufficient for most modelling tasks. With added monotonicity
constraints, a second hidden layer may sometimes be beneficial
(Lang, 2005; Minin et al., 2010). QRNN models with two hidden layers are
available using the qrnn2.fit and
qrnn2.predict functions. For non-crossing quantiles, the
mcqrnn.fit and mcqrnn.predict wrappers also allow
models with one or two hidden layers to be fitted and predictions to be made
from the fitted models.
In general, mcqrnn.fit offers a convenient, single function for
fitting multiple quantiles simultaneously. Note, however, that default
settings in mcqrnn.fit and other model fitting functions are
not optimized for general speed, memory efficiency, or accuracy and should be
adjusted for a particular regression problem as needed. In particular, the
approximation to the quantile regression cost function eps.seq, the
number of trials n.trials, and number of iterations iter.max
can all influence fitting speed (and accuracy), as can changing the
optimization algorithm via method. Non-crossing quantiles are
implemented by stacking multiple copies of the x and y data,
one copy per value of tau. Depending on the dataset size, this can
lead to large matrices being passed to the optimization routine. In the
adam adaptive stochastic gradient descent method, the
minibatch size can be adjusted to help offset this cost. Model complexity
is determined via the number of hidden nodes, n.hidden and
n.hidden2, as well as the optional weight penalty penalty; values
of these hyperparameters are crucial to obtaining a well performing model.
When using mcqrnn.fit, it is also possible to estimate the full
quantile regression process by specifying a single integer value for tau.
In this case, tau is the number of random samples used in the stochastic
estimation. For more information, see Tagasovska and Lopez-Paz (2019). It may be
necessary to restart the optimization multiple times from the previous weights
and biases, in which case init.range can be set to the weights
values from the previously completed optimization run. For large datasets, it is
recommended that the adam method with an appropriate integer
tau and minibatch size be used for optimization.
If models for multiple quantiles have been fitted, for example by
mcqrnn.fit or multiple calls to either qrnn.fit
or qrnn2.fit, the (experimental) dquantile
function and its companion functions are available to create proper
probability density, distribution, and quantile functions
(Quiñonero-Candela et al., 2006; Cannon, 2011). Alternative distribution,
quantile, and random variate functions based on the Nadaraya-Watson estimator
(Passow and Donner, 2020) are also available in [p,q,r]quantile.nw.
These can be useful for assessing probabilistic calibration and evaluating
model performance.
Note: the user cannot easily change the output layer transfer function
to be different than hramp, which provides either the identity function or a
ramp function to accommodate optional left censoring. Some applications, for
example fitting smoothed binary quantile regression models for a binary target
variable (Kordas, 2006), require an alternative like the logistic sigmoid.
While not straightforward, it is possible to change the output layer transfer
function by switching off scale.y in the call to the fitting
function and reassigning hramp and hramp.prime as follows:
library(qrnn)
# Use the logistic sigmoid as the output layer transfer function
To.logistic <- function(x, lower, eps) 0.5 + 0.5*tanh(x/2)
environment(To.logistic) <- asNamespace("qrnn")
assignInNamespace("hramp", To.logistic, ns="qrnn")
# Change the derivative of the output layer transfer function
To.logistic.prime <- function(x, lower, eps) 0.25/(cosh(x/2)^2)
environment(To.logistic.prime) <- asNamespace("qrnn")
assignInNamespace("hramp.prime", To.logistic.prime, ns="qrnn")
| Package: | qrnn |
| Type: | Package |
| License: | GPL-2 |
| LazyLoad: | yes |
Cannon, A.J., 2011. Quantile regression neural networks: implementation in R and application to precipitation downscaling. Computers & Geosciences, 37: 1277-1284. doi:10.1016/j.cageo.2010.07.005
Cannon, A.J., 2018. Non-crossing nonlinear regression quantiles by monotone composite quantile regression neural network, with application to rainfall extremes. Stochastic Environmental Research and Risk Assessment, 32(11): 3207-3225. doi:10.1007/s00477-018-1573-6
Chen, C., 2007. A finite smoothing algorithm for quantile regression. Journal of Computational and Graphical Statistics, 16: 136-164.
Friederichs, P. and A. Hense, 2007. Statistical downscaling of extreme precipitation events using censored quantile regression. Monthly Weather Review, 135: 2365-2378.
Jiang, X., J. Jiang, and X. Song, 2012. Oracle model selection for nonlinear models based on weighted composite quantile regression. Statistica Sinica, 22(4): 1479-1506.
Kordas, G., 2006. Smoothed binary regression quantiles. Journal of Applied Econometrics, 21(3): 387-407.
Lang, B., 2005. Monotonic multi-layer perceptron networks as universal approximators. International Conference on Artificial Neural Networks, Artificial Neural Networks: Formal Models and Their Applications-ICANN 2005, pp. 31-37.
Minin, A., M. Velikova, B. Lang, and H. Daniels, 2010. Comparison of universal approximators incorporating partial monotonicity by structure. Neural Networks, 23(4): 471-475.
Passow, C., R.V. Donner, 2020. Regression-based distribution mapping for bias correction of climate model outputs using linear quantile regression. Stochastic Environmental Research and Risk Assessment, 34: 87-102.
Plate, T., J. Bert, J. Grace, and P. Band, 2000. Visualizing the function computed by a feedforward neural network. Neural Computation, 12(6): 1337-1354.
Quiñonero-Candela, J., C. Rasmussen, F. Sinz, O. Bousquet, B. Scholkopf, 2006. Evaluating Predictive Uncertainty Challenge. Lecture Notes in Artificial Intelligence, 3944: 1-27.
Tagasovska, N., D. Lopez-Paz, 2019. Single-model uncertainties for deep learning. Advances in Neural Information Processing Systems, 32, NeurIPS 2019. doi:10.48550/arXiv.1811.00908
Taylor, J.W., 2000. A quantile regression neural network approach to estimating the conditional density of multiperiod returns. Journal of Forecasting, 19(4): 299-311.
Xu, Q., K. Deng, C. Jiang, F. Sun, and X. Huang, 2017. Composite quantile regression neural network with applications. Expert Systems with Applications, 76, 129-139.
Zhang, H. and Zhang, Z., 1999. Feedforward networks with monotone constraints. In: International Joint Conference on Neural Networks, vol. 3, p. 1820-1823. doi:10.1109/IJCNN.1999.832655
Zou, H. and M. Yuan, 2008. Composite quantile regression and the oracle model selection theory. The Annals of Statistics, 1108-1126.
From Kingma and Ba (2015): "We introduce Adam, an algorithm for first-order gradient-based optimization of stochastic objective functions, based on adaptive estimates of lower-order moments. The method is straightforward to implement, is computationally efficient, has little memory requirements, is invariant to diagonal rescaling of the gradients, and is well suited for problems that are large in terms of data and/or parameters. The method is also appropriate for non-stationary objectives and problems with very noisy and/or sparse gradients. The hyper-parameters have intuitive interpretations and typically require little tuning. Some connections to related algorithms, on which Adam was inspired, are discussed. We also analyze the theoretical convergence properties of the algorithm and provide a regret bound on the convergence rate that is comparable to the best known results under the online convex optimization framework. Empirical results demonstrate that Adam works well in practice and compares favorably to other stochastic optimization methods. Finally, we discuss AdaMax, a variant of Adam based on the infinity norm."
adam(f, p, x, y, w, tau, ..., iterlim=5000, iterbreak=iterlim, alpha=0.01, minibatch=nrow(x), beta1=0.9, beta2=0.999, epsilon=1e-8, print.level=10)adam(f, p, x, y, w, tau, ..., iterlim=5000, iterbreak=iterlim, alpha=0.01, minibatch=nrow(x), beta1=0.9, beta2=0.999, epsilon=1e-8, print.level=10)
f |
the function to be minimized, including gradient information
contained in the |
p |
the starting parameters for the minimization. |
x |
covariate matrix with number of rows equal to the number of samples and number of columns equal to the number of variables. |
y |
response column matrix with number of rows equal to the number of samples. |
w |
vector of weights with length equal to the number of samples. |
tau |
vector of desired tau-quantile(s) with length equal to the number of samples. |
... |
additional parameters passed to the |
iterlim |
the maximum number of iterations before the optimization is stopped. |
iterbreak |
the maximum number of iterations without progress before the optimization is stopped. |
alpha |
size of the learning rate. |
minibatch |
number of samples in each minibatch. |
beta1 |
controls the exponential decay rate used to scale the biased first moment estimate. |
beta2 |
controls the exponential decay rate used to scale the biased second raw moment estimate. |
epsilon |
smoothing term to avoid division by zero. |
print.level |
the level of printing which is done during optimization. A value of
|
A list with elements:
estimate |
The best set of parameters found. |
minimum |
The value of |
Kingma, D.P. and J. Ba, 2015. Adam: A method for stochastic optimization. The International Conference on Learning Representations (ICLR) 2015. http://arxiv.org/abs/1412.6980
Returns the median if the majority of values are censored and the mean otherwise.
censored.mean(x, lower, trim=0)censored.mean(x, lower, trim=0)
x |
numeric vector. |
lower |
left censoring point. |
trim |
fraction of observations to be trimmed from each end of |
x <- c(0, 0, 1, 2, 3) print(censored.mean(x, lower=0)) x.cens <- c(0, 0, 0, 1, 2) print(censored.mean(x.cens, lower=0))x <- c(0, 0, 1, 2, 3) print(censored.mean(x, lower=0)) x.cens <- c(0, 0, 0, 1, 2) print(censored.mean(x.cens, lower=0))
Returns stacked x and y matrices and tau vector,
which can be passed to qrnn.fit to fit composite quantile
regression and composite QRNN models (Zou et al., 2008;
Xu et al., 2017). In combination with the partial monotonicity
constraints, stacking can be used to fit multiple non-crossing
quantile functions (see mcqrnn). More details
are provided in Cannon (2018).
composite.stack(x, y, tau)composite.stack(x, y, tau)
x |
covariate matrix with number of rows equal to the number of samples and number of columns equal to the number of variables. |
y |
response column matrix with number of rows equal to the number of samples. |
tau |
vector of tau-quantiles. |
Cannon, A.J., 2018. Non-crossing nonlinear regression quantiles by monotone composite quantile regression neural network, with application to rainfall extremes. Stochastic Environmental Research and Risk Assessment, 32(11): 3207-3225. doi:10.1007/s00477-018-1573-6
Xu, Q., K. Deng, C. Jiang, F. Sun, and X. Huang, 2017. Composite quantile regression neural network with applications. Expert Systems with Applications, 76, 129-139.
Zou, H. and M. Yuan, 2008. Composite quantile regression and the oracle model selection theory. The Annals of Statistics, 1108-1126.
x <- as.matrix(iris[,"Petal.Length",drop=FALSE]) y <- as.matrix(iris[,"Petal.Width",drop=FALSE]) cases <- order(x) x <- x[cases,,drop=FALSE] y <- y[cases,,drop=FALSE] tau <- seq(0.05, 0.95, by=0.05) x.y.tau <- composite.stack(x, y, tau) binary.tau <- dummy.code(as.factor(x.y.tau$tau)) set.seed(1) # Composite QR fit.cqr <- qrnn.fit(cbind(binary.tau, x.y.tau$x), x.y.tau$y, tau=x.y.tau$tau, n.hidden=1, n.trials=1, Th=linear, Th.prime=linear.prime) pred.cqr <- matrix(qrnn.predict(cbind(binary.tau, x.y.tau$x), fit.cqr), ncol=length(tau)) coef.cqr <- lm.fit(cbind(1, x), pred.cqr)$coef colnames(coef.cqr) <- tau print(coef.cqr) # Composite QRNN fit.cqrnn <- qrnn.fit(x.y.tau$x, x.y.tau$y, tau=x.y.tau$tau, n.hidden=1, n.trials=1, Th=sigmoid, Th.prime=sigmoid.prime) pred.cqrnn <- qrnn.predict(x.y.tau$x, fit.cqrnn) pred.cqrnn <- matrix(pred.cqrnn, ncol=length(tau), byrow=FALSE) matplot(x, pred.cqrnn, col="red", type="l") points(x, y, pch=20)x <- as.matrix(iris[,"Petal.Length",drop=FALSE]) y <- as.matrix(iris[,"Petal.Width",drop=FALSE]) cases <- order(x) x <- x[cases,,drop=FALSE] y <- y[cases,,drop=FALSE] tau <- seq(0.05, 0.95, by=0.05) x.y.tau <- composite.stack(x, y, tau) binary.tau <- dummy.code(as.factor(x.y.tau$tau)) set.seed(1) # Composite QR fit.cqr <- qrnn.fit(cbind(binary.tau, x.y.tau$x), x.y.tau$y, tau=x.y.tau$tau, n.hidden=1, n.trials=1, Th=linear, Th.prime=linear.prime) pred.cqr <- matrix(qrnn.predict(cbind(binary.tau, x.y.tau$x), fit.cqr), ncol=length(tau)) coef.cqr <- lm.fit(cbind(1, x), pred.cqr)$coef colnames(coef.cqr) <- tau print(coef.cqr) # Composite QRNN fit.cqrnn <- qrnn.fit(x.y.tau$x, x.y.tau$y, tau=x.y.tau$tau, n.hidden=1, n.trials=1, Th=sigmoid, Th.prime=sigmoid.prime) pred.cqrnn <- qrnn.predict(x.y.tau$x, fit.cqrnn) pred.cqrnn <- matrix(pred.cqrnn, ncol=length(tau), byrow=FALSE) matplot(x, pred.cqrnn, col="red", type="l") points(x, y, pch=20)
Converts a factor (categorical) variable to a matrix of dummy codes using a 1 of C-1 binary coding scheme.
dummy.code(x)dummy.code(x)
x |
a factor variable. |
a matrix with the number of rows equal to the number of cases in x
and the number of columns equal to one minus the number of factors in
x. The last factor serves as the reference group.
print(dummy.code(iris$Species))print(dummy.code(iris$Species))
Generalized additive model (GAM)-style effects plots provide a graphical
means of interpreting relationships between covariates and conditional
quantiles predicted by a QRNN. From Plate et al. (2000): The effect of the
ith input variable at a particular input point Delta.i.x
is the change in f resulting from changing X1 to x1
from b1 (the baseline value [...]) while keeping the other
inputs constant. The effects are plotted as short line segments, centered
at (x.i, Delta.i.x), where the slope of the segment
is given by the partial derivative. Variables that strongly influence
the function value have a large total vertical range of effects.
Functions without interactions appear as possibly broken straight lines
(linear functions) or curves (nonlinear functions). Interactions show up as
vertical spread at a particular horizontal location, that is, a vertical
scattering of segments. Interactions are present when the effect of
a variable depends on the values of other variables.
gam.style(x, parms, column, baseline=mean(x[,column]), epsilon=1e-5, seg.len=0.02, seg.cols="black", plot=TRUE, return.results=FALSE, trim=0, ...)gam.style(x, parms, column, baseline=mean(x[,column]), epsilon=1e-5, seg.len=0.02, seg.cols="black", plot=TRUE, return.results=FALSE, trim=0, ...)
x |
matrix with number of rows equal to the number of samples and number of columns equal to the number of covariate variables. |
parms |
list returned by |
column |
column of |
baseline |
value of |
epsilon |
step-size used in the finite difference calculation of the partial derivatives. |
seg.len |
length of effects line segments expressed as a fraction of the range of |
seg.cols |
colors of effects line segments. |
plot |
if |
return.results |
if |
trim |
if |
... |
further arguments to be passed to |
A list with elements:
effects |
a matrix of covariate effects. |
partials |
a matrix of covariate partial derivatives. |
Cannon, A.J. and I.G. McKendry, 2002. A graphical sensitivity analysis for interpreting statistical climate models: Application to Indian monsoon rainfall prediction by artificial neural networks and multiple linear regression models. International Journal of Climatology, 22:1687-1708.
Plate, T., J. Bert, J. Grace, and P. Band, 2000. Visualizing the function computed by a feedforward neural network. Neural Computation, 12(6): 1337-1354.
## YVR precipitation data with seasonal cycle and NCEP/NCAR Reanalysis ## covariates data(YVRprecip) y <- YVRprecip$precip x <- cbind(sin(2*pi*seq_along(y)/365.25), cos(2*pi*seq_along(y)/365.25), YVRprecip$ncep) ## Fit QRNN, additive QRNN (QADD), and quantile regression (QREG) ## models for the conditional 75th percentile set.seed(1) train <- c(TRUE, rep(FALSE, 49)) w.qrnn <- qrnn.fit(x=x[train,], y=y[train,,drop=FALSE], n.hidden=2, tau=0.75, iter.max=500, n.trials=1, lower=0, penalty=0.01) w.qadd <- qrnn.fit(x=x[train,], y=y[train,,drop=FALSE], n.hidden=ncol(x), tau=0.75, iter.max=250, n.trials=1, lower=0, additive=TRUE) w.qreg <- qrnn.fit(x=x[train,], y=y[train,,drop=FALSE], tau=0.75, iter.max=100, n.trials=1, lower=0, Th=linear, Th.prime=linear.prime) ## GAM-style plots for slp, sh700, and z500 for (column in 3:5) { gam.style(x[train,], parms=w.qrnn, column=column, main="QRNN") gam.style(x[train,], parms=w.qadd, column=column, main="QADD") gam.style(x[train,], parms=w.qreg, column=column, main="QREG") }## YVR precipitation data with seasonal cycle and NCEP/NCAR Reanalysis ## covariates data(YVRprecip) y <- YVRprecip$precip x <- cbind(sin(2*pi*seq_along(y)/365.25), cos(2*pi*seq_along(y)/365.25), YVRprecip$ncep) ## Fit QRNN, additive QRNN (QADD), and quantile regression (QREG) ## models for the conditional 75th percentile set.seed(1) train <- c(TRUE, rep(FALSE, 49)) w.qrnn <- qrnn.fit(x=x[train,], y=y[train,,drop=FALSE], n.hidden=2, tau=0.75, iter.max=500, n.trials=1, lower=0, penalty=0.01) w.qadd <- qrnn.fit(x=x[train,], y=y[train,,drop=FALSE], n.hidden=ncol(x), tau=0.75, iter.max=250, n.trials=1, lower=0, additive=TRUE) w.qreg <- qrnn.fit(x=x[train,], y=y[train,,drop=FALSE], tau=0.75, iter.max=100, n.trials=1, lower=0, Th=linear, Th.prime=linear.prime) ## GAM-style plots for slp, sh700, and z500 for (column in 3:5) { gam.style(x[train,], parms=w.qrnn, column=column, main="QRNN") gam.style(x[train,], parms=w.qadd, column=column, main="QADD") gam.style(x[train,], parms=w.qreg, column=column, main="QREG") }
Huber norm function providing a hybrid L1/L2 norm. Huber approximations to the ramp hramp and tilted absolute value tilted.approx functions. huber.prime, hramp.prime, and tilted.approx.prime provide the corresponding derivatives.
huber(x, eps) huber.prime(x, eps) hramp(x, lower, eps) hramp.prime(x, lower, eps) tilted.approx(x, tau, eps) tilted.approx.prime(x, tau, eps)huber(x, eps) huber.prime(x, eps) hramp(x, lower, eps) hramp.prime(x, lower, eps) tilted.approx(x, tau, eps) tilted.approx.prime(x, tau, eps)
x |
numeric vector. |
eps |
epsilon value used in |
tau |
desired tau-quantile. |
lower |
left censoring point. |
x <- seq(-10, 10, length=100) plot(x, huber(x, eps=1), type="l", col="black", ylim=c(-2, 10), ylab="") lines(x, hramp(x, lower=0, eps=1), col="red") lines(x, tilted.approx(x, tau=0.1, eps=1), col="blue") lines(x, huber.prime(x, eps=1), col="black", lty=2) lines(x, hramp.prime(x, lower=0, eps=1), lty=2, col="red") lines(x, tilted.approx.prime(x, tau=0.1, eps=1), lty=2, col="blue")x <- seq(-10, 10, length=100) plot(x, huber(x, eps=1), type="l", col="black", ylim=c(-2, 10), ylab="") lines(x, hramp(x, lower=0, eps=1), col="red") lines(x, tilted.approx(x, tau=0.1, eps=1), col="blue") lines(x, huber.prime(x, eps=1), col="black", lty=2) lines(x, hramp.prime(x, lower=0, eps=1), lty=2, col="red") lines(x, tilted.approx.prime(x, tau=0.1, eps=1), lty=2, col="blue")
High level wrapper functions for fitting and making predictions from a monotone composite quantile regression neural network (MCQRNN) model for multiple non-crossing regression quantiles (Cannon, 2018).
Uses composite.stack and monotonicity constraints in
qrnn.fit or qrnn2.fit to fit MCQRNN models with
one or two hidden layers. Note: Th must be a non-decreasing
function to guarantee non-crossing.
Following Tagasovska and Lopez-Paz (2019), it is also possible to estimate the
full quantile regression process by specifying a single integer value for
tau. In this case, tau is the number of random samples used in the
stochastic estimation. It may be necessary to restart the optimization multiple
times from the previous weights and biases, in which case init.range can
be set to the weights values from the previously completed optimization run.
For large datasets, it is recommended that the adam method with an
appropriate minibatch size be used for optimization.
mcqrnn.fit(x, y, n.hidden=2, n.hidden2=NULL, w=NULL, tau=c(0.1, 0.5, 0.9), iter.max=5000, n.trials=5, lower=-Inf, init.range=c(-0.5, 0.5, -0.5, 0.5, -0.5, 0.5), monotone=NULL, eps.seq=2^seq(-8, -32, by=-4), Th=sigmoid, Th.prime=sigmoid.prime, penalty=0, n.errors.max=10, trace=TRUE, method=c("nlm", "adam"), scale.y=TRUE, ...) mcqrnn.predict(x, parms, tau=NULL)mcqrnn.fit(x, y, n.hidden=2, n.hidden2=NULL, w=NULL, tau=c(0.1, 0.5, 0.9), iter.max=5000, n.trials=5, lower=-Inf, init.range=c(-0.5, 0.5, -0.5, 0.5, -0.5, 0.5), monotone=NULL, eps.seq=2^seq(-8, -32, by=-4), Th=sigmoid, Th.prime=sigmoid.prime, penalty=0, n.errors.max=10, trace=TRUE, method=c("nlm", "adam"), scale.y=TRUE, ...) mcqrnn.predict(x, parms, tau=NULL)
x |
covariate matrix with number of rows equal to the number of samples and number of columns equal to the number of variables. |
y |
response column matrix with number of rows equal to the number of samples. |
|
number of hidden nodes in the first hidden layer. |
|
|
number of hidden nodes in the second hidden layer; |
|
w |
if |
tau |
desired tau-quantiles; |
iter.max |
maximum number of iterations of the optimization algorithm. |
n.trials |
number of repeated trials used to avoid local minima. |
lower |
left censoring point. |
init.range |
initial weight range for input-hidden, hidden-hidden, and hidden-output weight matrices. If supplied with a list
of weight matrices from a prior run of |
monotone |
column indices of covariates for which the monotonicity constraint should hold. |
eps.seq |
sequence of |
Th |
hidden layer transfer function; use |
Th.prime |
derivative of the hidden layer transfer function |
penalty |
weight penalty for weight decay regularization. |
n.errors.max |
maximum number of |
trace |
logical variable indicating whether or not diagnostic messages are printed during optimization. |
method |
character string indicating which optimization algorithm to use when |
scale.y |
logical variable indicating whether |
... |
additional parameters passed to the |
parms |
list containing MCQRNN weight matrices and other parameters. |
Cannon, A.J., 2011. Quantile regression neural networks: implementation in R and application to precipitation downscaling. Computers & Geosciences, 37: 1277-1284. doi:10.1016/j.cageo.2010.07.005
Cannon, A.J., 2018. Non-crossing nonlinear regression quantiles by monotone composite quantile regression neural network, with application to rainfall extremes. Stochastic Environmental Research and Risk Assessment, 32(11): 3207-3225. doi:10.1007/s00477-018-1573-6
Tagasovska, N., D. Lopez-Paz, 2019. Single-model uncertainties for deep learning. Advances in Neural Information Processing Systems, 32, NeurIPS 2019. doi:10.48550/arXiv.1811.00908
composite.stack, qrnn.fit,
qrnn2.fit, qrnn.predict,
qrnn2.predict, adam
x <- as.matrix(iris[,"Petal.Length",drop=FALSE]) y <- as.matrix(iris[,"Petal.Width",drop=FALSE]) cases <- order(x) x <- x[cases,,drop=FALSE] y <- y[cases,,drop=FALSE] set.seed(1) ## MCQRNN model w/ 2 hidden layers for simultaneous estimation of ## multiple non-crossing quantile functions fit.mcqrnn <- mcqrnn.fit(x, y, tau=seq(0.1, 0.9, by=0.1), n.hidden=2, n.hidden2=2, n.trials=1, iter.max=500) pred.mcqrnn <- mcqrnn.predict(x, fit.mcqrnn) ## Estimate the full quantile regression process by specifying ## the number of samples/random values of tau used in training fit.full <- mcqrnn.fit(x, y, tau=1000L, n.hidden=3, n.hidden2=3, n.trials=1, iter.max=300, eps.seq=1e-6, method="adam", minibatch=64, print.level=100) # Show how to initialize from previous weights fit.full <- mcqrnn.fit(x, y, tau=1000L, n.hidden=3, n.hidden2=3, n.trials=1, iter.max=300, eps.seq=1e-6, method="adam", minibatch=64, print.level=100, init.range=fit.full$weights) pred.full <- mcqrnn.predict(x, fit.full, tau=seq(0.1, 0.9, by=0.1)) par(mfrow=c(1, 2)) matplot(x, pred.mcqrnn, col="blue", type="l") points(x, y) matplot(x, pred.full, col="blue", type="l") points(x, y)x <- as.matrix(iris[,"Petal.Length",drop=FALSE]) y <- as.matrix(iris[,"Petal.Width",drop=FALSE]) cases <- order(x) x <- x[cases,,drop=FALSE] y <- y[cases,,drop=FALSE] set.seed(1) ## MCQRNN model w/ 2 hidden layers for simultaneous estimation of ## multiple non-crossing quantile functions fit.mcqrnn <- mcqrnn.fit(x, y, tau=seq(0.1, 0.9, by=0.1), n.hidden=2, n.hidden2=2, n.trials=1, iter.max=500) pred.mcqrnn <- mcqrnn.predict(x, fit.mcqrnn) ## Estimate the full quantile regression process by specifying ## the number of samples/random values of tau used in training fit.full <- mcqrnn.fit(x, y, tau=1000L, n.hidden=3, n.hidden2=3, n.trials=1, iter.max=300, eps.seq=1e-6, method="adam", minibatch=64, print.level=100) # Show how to initialize from previous weights fit.full <- mcqrnn.fit(x, y, tau=1000L, n.hidden=3, n.hidden2=3, n.trials=1, iter.max=300, eps.seq=1e-6, method="adam", minibatch=64, print.level=100, init.range=fit.full$weights) pred.full <- mcqrnn.predict(x, fit.full, tau=seq(0.1, 0.9, by=0.1)) par(mfrow=c(1, 2)) matplot(x, pred.mcqrnn, col="blue", type="l") points(x, y) matplot(x, pred.full, col="blue", type="l") points(x, y)
Smooth approximation to the tilted absolute value cost function used to fit a QRNN model. Optional left censoring, monotone constraints, and additive constraints are supported.
qrnn.cost(weights, x, y, n.hidden, w, tau, lower, monotone, additive, eps, Th, Th.prime, penalty, unpenalized)qrnn.cost(weights, x, y, n.hidden, w, tau, lower, monotone, additive, eps, Th, Th.prime, penalty, unpenalized)
weights |
weight vector of length returned by |
x |
covariate matrix with number of rows equal to the number of samples and number of columns equal to the number of variables. |
y |
response column matrix with number of rows equal to the number of samples. |
|
number of hidden nodes in the QRNN model. |
|
w |
vector of weights with length equal to the number of samples;
|
tau |
desired tau-quantile. |
lower |
left censoring point. |
monotone |
column indices of covariates for which the monotonicity constraint should hold. |
additive |
force additive relationships. |
eps |
epsilon value used in the approximation functions. |
Th |
hidden layer transfer function; use |
Th.prime |
derivative of the hidden layer transfer function |
penalty |
weight penalty for weight decay regularization. |
unpenalized |
column indices of covariates for which the weight penalty should not be applied to input-hidden layer weights. |
numeric value indicating tilted absolute value cost function, along with attribute containing vector with gradient information.
Function used to fit a QRNN model or ensemble of QRNN models.
qrnn.fit(x, y, n.hidden, w=NULL, tau=0.5, n.ensemble=1, iter.max=5000, n.trials=5, bag=FALSE, lower=-Inf, init.range=c(-0.5, 0.5, -0.5, 0.5), monotone=NULL, additive=FALSE, eps.seq=2^seq(-8, -32, by=-4), Th=sigmoid, Th.prime=sigmoid.prime, penalty=0, unpenalized=NULL, n.errors.max=10, trace=TRUE, scale.y=TRUE, ...)qrnn.fit(x, y, n.hidden, w=NULL, tau=0.5, n.ensemble=1, iter.max=5000, n.trials=5, bag=FALSE, lower=-Inf, init.range=c(-0.5, 0.5, -0.5, 0.5), monotone=NULL, additive=FALSE, eps.seq=2^seq(-8, -32, by=-4), Th=sigmoid, Th.prime=sigmoid.prime, penalty=0, unpenalized=NULL, n.errors.max=10, trace=TRUE, scale.y=TRUE, ...)
x |
covariate matrix with number of rows equal to the number of samples and number of columns equal to the number of variables. |
y |
response column matrix with number of rows equal to the number of samples. |
|
number of hidden nodes in the QRNN model. |
|
w |
vector of weights with length equal to the number of samples;
|
tau |
desired tau-quantile(s). |
n.ensemble |
number of ensemble members to fit. |
iter.max |
maximum number of iterations of the optimization algorithm. |
n.trials |
number of repeated trials used to avoid local minima. |
bag |
logical variable indicating whether or not bootstrap aggregation (bagging) should be used. |
lower |
left censoring point. |
init.range |
initial weight range for input-hidden and hidden-output weight matrices. |
monotone |
column indices of covariates for which the monotonicity constraint should hold. |
additive |
force additive relationships. |
eps.seq |
sequence of |
Th |
hidden layer transfer function; use |
Th.prime |
derivative of the hidden layer transfer function |
penalty |
weight penalty for weight decay regularization. |
unpenalized |
column indices of covariates for which the weight penalty should not be applied to input-hidden layer weights. |
n.errors.max |
maximum number of |
trace |
logical variable indicating whether or not diagnostic messages are printed during optimization. |
scale.y |
logical variable indicating whether |
... |
additional parameters passed to the |
Fit a censored quantile regression neural network model for the
tau-quantile by minimizing a cost function based on smooth
Huber-norm approximations to the tilted absolute value and ramp functions.
Left censoring can be turned on by setting lower to a value
greater than -Inf. A simplified form of the finite smoothing
algorithm, in which the nlm optimization algorithm
is run with values of the eps approximation tolerance progressively
reduced in magnitude over the sequence eps.seq, is used to set the
QRNN weights and biases. Local minima of the cost function can be
avoided by setting n.trials, which controls the number of
repeated runs from different starting weights and biases, to a value
greater than one.
(Note: if eps.seq is set to a single, sufficiently large value and tau
is set to 0.5, then the result will be a standard least squares
regression model. The same value of eps.seq and other values
of tau leads to expectile regression.)
If invoked, the monotone argument enforces non-decreasing behaviour
between specified columns of x and model outputs. This holds if
Th and To are monotone non-decreasing functions. In this case,
the exp function is applied to the relevant weights following
initialization and during optimization; manual adjustment of
init.weights or qrnn.initialize may be needed due to
differences in scaling of the constrained and unconstrained weights.
Non-increasing behaviour can be forced by transforming the relevant
covariates, e.g., by reversing sign.
The additive argument sets relevant input-hidden layer weights
to zero, resulting in a purely additive model. Interactions between covariates
are thus suppressed, leading to a compromise in flexibility between
linear quantile regression and the quantile regression neural network.
Borrowing strength by using a composite model for multiple regression quantiles
is also possible (see composite.stack). Applying the monotone
constraint in combination with the composite model allows
one to simultaneously estimate multiple non-crossing quantiles;
the resulting monotone composite QRNN (MCQRNN) is demonstrated in
mcqrnn.
In the linear case, model complexity does not depend on the number
of hidden nodes; the value of n.hidden is ignored and is instead
set to one internally. In the nonlinear case, n.hidden
controls the overall complexity of the model. As an added means of
avoiding overfitting, weight penalty regularization for the magnitude
of the input-hidden layer weights (excluding biases) can be applied
by setting penalty to a nonzero value. (For the linear model,
this penalizes both input-hidden and hidden-output layer weights,
leading to a quantile ridge regression model. In this case, kernel
quantile ridge regression can be performed with the aid of the
qrnn.rbf function.) Finally, if the bag argument
is set to TRUE, models are trained on bootstrapped x and
y sample pairs; bootstrap aggregation (bagging) can be turned
on by setting n.ensemble to a value greater than one. Averaging
over an ensemble of bagged models will also tend to alleviate
overfitting.
The gam.style function can be used to plot modified
generalized additive model effects plots, which are useful for visualizing
the modelled covariate-response relationships.
Note: values of x and y need not be standardized or
rescaled by the user. All variables are automatically scaled to zero
mean and unit standard deviation prior to fitting and parameters are
automatically rescaled by qrnn.predict and other prediction
functions. Values of eps.seq are relative to the residuals in
standard deviation units. Note: scaling of y can be turned off using
the scale.y argument.
a list containing elements
weights |
a list containing fitted weight matrices |
lower |
left censoring point |
eps.seq |
sequence of |
tau |
desired tau-quantile(s) |
Th |
hidden layer transfer function |
x.center |
vector of column means for |
x.scale |
vector of column standard deviations for |
y.center |
vector of column means for |
y.scale |
vector of column standard deviations for |
monotone |
column indices indicating covariate monotonicity constraints. |
additive |
force additive relationships. |
Cannon, A.J., 2011. Quantile regression neural networks: implementation in R and application to precipitation downscaling. Computers & Geosciences, 37: 1277-1284. doi:10.1016/j.cageo.2010.07.005
Cannon, A.J., 2018. Non-crossing nonlinear regression quantiles by monotone composite quantile regression neural network, with application to rainfall extremes. Stochastic Environmental Research and Risk Assessment, 32(11): 3207-3225. doi:10.1007/s00477-018-1573-6
qrnn.predict, qrnn.cost, composite.stack, mcqrnn, gam.style
x <- as.matrix(iris[,"Petal.Length",drop=FALSE]) y <- as.matrix(iris[,"Petal.Width",drop=FALSE]) cases <- order(x) x <- x[cases,,drop=FALSE] y <- y[cases,,drop=FALSE] tau <- c(0.05, 0.5, 0.95) set.seed(1) ## QRNN models for conditional 5th, 50th, and 95th percentiles w <- p <- vector("list", length(tau)) for(i in seq_along(tau)){ w[[i]] <- qrnn.fit(x=x, y=y, n.hidden=3, tau=tau[i], iter.max=200, n.trials=1) p[[i]] <- qrnn.predict(x, w[[i]]) } ## Monotone composite QRNN (MCQRNN) for simultaneous estimation of ## multiple non-crossing quantile functions x.y.tau <- composite.stack(x, y, tau) fit.mcqrnn <- qrnn.fit(cbind(x.y.tau$tau, x.y.tau$x), x.y.tau$y, tau=x.y.tau$tau, n.hidden=3, n.trials=1, iter.max=500, monotone=1) pred.mcqrnn <- matrix(qrnn.predict(cbind(x.y.tau$tau, x.y.tau$x), fit.mcqrnn), ncol=length(tau)) par(mfrow=c(1, 2)) matplot(x, matrix(unlist(p), nrow=nrow(x), ncol=length(p)), col="red", type="l") points(x, y) matplot(x, pred.mcqrnn, col="blue", type="l") points(x, y)x <- as.matrix(iris[,"Petal.Length",drop=FALSE]) y <- as.matrix(iris[,"Petal.Width",drop=FALSE]) cases <- order(x) x <- x[cases,,drop=FALSE] y <- y[cases,,drop=FALSE] tau <- c(0.05, 0.5, 0.95) set.seed(1) ## QRNN models for conditional 5th, 50th, and 95th percentiles w <- p <- vector("list", length(tau)) for(i in seq_along(tau)){ w[[i]] <- qrnn.fit(x=x, y=y, n.hidden=3, tau=tau[i], iter.max=200, n.trials=1) p[[i]] <- qrnn.predict(x, w[[i]]) } ## Monotone composite QRNN (MCQRNN) for simultaneous estimation of ## multiple non-crossing quantile functions x.y.tau <- composite.stack(x, y, tau) fit.mcqrnn <- qrnn.fit(cbind(x.y.tau$tau, x.y.tau$x), x.y.tau$y, tau=x.y.tau$tau, n.hidden=3, n.trials=1, iter.max=500, monotone=1) pred.mcqrnn <- matrix(qrnn.predict(cbind(x.y.tau$tau, x.y.tau$x), fit.mcqrnn), ncol=length(tau)) par(mfrow=c(1, 2)) matplot(x, matrix(unlist(p), nrow=nrow(x), ncol=length(p)), col="red", type="l") points(x, y) matplot(x, pred.mcqrnn, col="blue", type="l") points(x, y)
Random initialization of the weight vector used during fitting of a QRNN model.
qrnn.initialize(x, y, n.hidden, init.range=c(-0.5, 0.5, -0.5, 0.5))qrnn.initialize(x, y, n.hidden, init.range=c(-0.5, 0.5, -0.5, 0.5))
x |
covariate matrix with number of rows equal to the number of samples and number of columns equal to the number of variables. |
y |
response column matrix with number of rows equal to the number of samples. |
|
number of hidden nodes in the QRNN model. |
|
init.range |
initial weight range for input-hidden and hidden-output weight matrices. |
Evaluate a fitted QRNN model or ensemble of models, resulting in a list containing the predicted quantiles.
qrnn.predict(x, parms)qrnn.predict(x, parms)
x |
covariate matrix with number of rows equal to the number of samples and number of columns equal to the number of variables. |
parms |
list containing QRNN input-hidden and hidden-output layer weight matrices and other parameters from |
a list with number of elements equal to that of parms, each containing a column matrix of predicted quantiles.
x <- as.matrix(iris[,"Petal.Length",drop=FALSE]) y <- as.matrix(iris[,"Petal.Width",drop=FALSE]) cases <- order(x) x <- x[cases,,drop=FALSE] y <- y[cases,,drop=FALSE] y[y < 0.5] <- 0.5 set.seed(1) parms <- qrnn.fit(x=x, y=y, n.hidden=3, tau=0.5, lower=0.5, iter.max=500, n.trials=1) p <- qrnn.predict(x=x, parms=parms) matplot(x, cbind(y, p), type=c("p", "l"), pch=1, lwd=1)x <- as.matrix(iris[,"Petal.Length",drop=FALSE]) y <- as.matrix(iris[,"Petal.Width",drop=FALSE]) cases <- order(x) x <- x[cases,,drop=FALSE] y <- y[cases,,drop=FALSE] y[y < 0.5] <- 0.5 set.seed(1) parms <- qrnn.fit(x=x, y=y, n.hidden=3, tau=0.5, lower=0.5, iter.max=500, n.trials=1) p <- qrnn.predict(x=x, parms=parms) matplot(x, cbind(y, p), type=c("p", "l"), pch=1, lwd=1)
Evaluate a kernel matrix based on the radial basis function kernel. Can
be used in conjunction with qrnn.fit with Th set to
linear and penalty set to a nonzero value for
kernel quantile ridge regression.
qrnn.rbf(x, x.basis, sigma)qrnn.rbf(x, x.basis, sigma)
x |
covariate matrix with number of rows equal to the number of samples and number of columns equal to the number of variables. |
x.basis |
covariate matrix with number of rows equal to the number of basis functions and number of columns equal to the number of variables. |
sigma |
kernel width |
kernel matrix with number of rows equal to the number of samples and number of columns equal to the number of basis functions.
x <- as.matrix(iris[,"Petal.Length",drop=FALSE]) y <- as.matrix(iris[,"Petal.Width",drop=FALSE]) cases <- order(x) x <- x[cases,,drop=FALSE] y <- y[cases,,drop=FALSE] set.seed(1) kern <- qrnn.rbf(x, x.basis=x, sigma=1) parms <- qrnn.fit(x=kern, y=y, tau=0.5, penalty=0.1, Th=linear, Th.prime=linear.prime, iter.max=500, n.trials=1) p <- qrnn.predict(x=kern, parms=parms) matplot(x, cbind(y, p), type=c("p", "l"), pch=1, lwd=1)x <- as.matrix(iris[,"Petal.Length",drop=FALSE]) y <- as.matrix(iris[,"Petal.Width",drop=FALSE]) cases <- order(x) x <- x[cases,,drop=FALSE] y <- y[cases,,drop=FALSE] set.seed(1) kern <- qrnn.rbf(x, x.basis=x, sigma=1) parms <- qrnn.fit(x=kern, y=y, tau=0.5, penalty=0.1, Th=linear, Th.prime=linear.prime, iter.max=500, n.trials=1) p <- qrnn.predict(x=kern, parms=parms) matplot(x, cbind(y, p), type=c("p", "l"), pch=1, lwd=1)
Functions used to fit and make predictions from QRNN models with two hidden layers.
Note: Th must be a non-decreasing function if monotone != NULL.
qrnn2.fit(x, y, n.hidden=2, n.hidden2=2, w=NULL, tau=0.5, n.ensemble=1, iter.max=5000, n.trials=5, bag=FALSE, lower=-Inf, init.range=c(-0.5, 0.5, -0.5, 0.5, -0.5, 0.5), monotone=NULL, eps.seq=2^seq(-8, -32, by=-4), Th=sigmoid, Th.prime=sigmoid.prime, penalty=0, unpenalized=NULL, n.errors.max=10, trace=TRUE, method=c("nlm", "adam"), scale.y=TRUE, ...) qrnn2.predict(x, parms)qrnn2.fit(x, y, n.hidden=2, n.hidden2=2, w=NULL, tau=0.5, n.ensemble=1, iter.max=5000, n.trials=5, bag=FALSE, lower=-Inf, init.range=c(-0.5, 0.5, -0.5, 0.5, -0.5, 0.5), monotone=NULL, eps.seq=2^seq(-8, -32, by=-4), Th=sigmoid, Th.prime=sigmoid.prime, penalty=0, unpenalized=NULL, n.errors.max=10, trace=TRUE, method=c("nlm", "adam"), scale.y=TRUE, ...) qrnn2.predict(x, parms)
x |
covariate matrix with number of rows equal to the number of samples and number of columns equal to the number of variables. |
y |
response column matrix with number of rows equal to the number of samples. |
|
number of hidden nodes in the first hidden layer. |
|
|
number of hidden nodes in the second hidden layer. |
|
w |
vector of weights with length equal to the number of samples;
|
tau |
desired tau-quantile(s). |
n.ensemble |
number of ensemble members to fit. |
iter.max |
maximum number of iterations of the optimization algorithm. |
n.trials |
number of repeated trials used to avoid local minima. |
bag |
logical variable indicating whether or not bootstrap aggregation (bagging) should be used. |
lower |
left censoring point. |
init.range |
initial weight range for input-hidden, hidden-hidden, and hidden-output weight matrices. |
monotone |
column indices of covariates for which the monotonicity constraint should hold. |
eps.seq |
sequence of |
Th |
hidden layer transfer function; use |
Th.prime |
derivative of the hidden layer transfer function |
penalty |
weight penalty for weight decay regularization. |
unpenalized |
column indices of covariates for which the weight penalty should not be applied to input-hidden layer weights. |
n.errors.max |
maximum number of |
trace |
logical variable indicating whether or not diagnostic messages are printed during optimization. |
method |
character string indicating which optimization algorithm to use. |
scale.y |
logical variable indicating whether |
... |
additional parameters passed to the |
parms |
list containing QRNN weight matrices and other parameters from |
Cannon, A.J., 2011. Quantile regression neural networks: implementation in R and application to precipitation downscaling. Computers & Geosciences, 37: 1277-1284. doi:10.1016/j.cageo.2010.07.005
Cannon, A.J., 2018. Non-crossing nonlinear regression quantiles by monotone composite quantile regression neural network, with application to rainfall extremes. Stochastic Environmental Research and Risk Assessment, 32(11): 3207-3225. doi:10.1007/s00477-018-1573-6
qrnn.fit, qrnn.predict,
qrnn.cost, composite.stack,
mcqrnn, adam
x <- as.matrix(iris[,"Petal.Length",drop=FALSE]) y <- as.matrix(iris[,"Petal.Width",drop=FALSE]) cases <- order(x) x <- x[cases,,drop=FALSE] y <- y[cases,,drop=FALSE] tau <- c(0.05, 0.5, 0.95) set.seed(1) ## QRNN models w/ 2 hidden layers (tau=0.05, 0.50, 0.95) w <- p <- vector("list", length(tau)) for(i in seq_along(tau)){ w[[i]] <- qrnn2.fit(x=x, y=y, n.hidden=3, n.hidden2=3, tau=tau[i], iter.max=200, n.trials=1) p[[i]] <- qrnn2.predict(x, w[[i]]) } ## MCQRNN model w/ 2 hidden layers for simultaneous estimation of ## multiple non-crossing quantile functions x.y.tau <- composite.stack(x, y, tau) fit.mcqrnn <- qrnn2.fit(cbind(x.y.tau$tau, x.y.tau$x), x.y.tau$y, tau=x.y.tau$tau, n.hidden=3, n.hidden2=3, n.trials=1, iter.max=500, monotone=1) pred.mcqrnn <- matrix(qrnn2.predict(cbind(x.y.tau$tau, x.y.tau$x), fit.mcqrnn), ncol=length(tau)) par(mfrow=c(1, 2)) matplot(x, matrix(unlist(p), nrow=nrow(x), ncol=length(p)), col="red", type="l") points(x, y) matplot(x, pred.mcqrnn, col="blue", type="l") points(x, y)x <- as.matrix(iris[,"Petal.Length",drop=FALSE]) y <- as.matrix(iris[,"Petal.Width",drop=FALSE]) cases <- order(x) x <- x[cases,,drop=FALSE] y <- y[cases,,drop=FALSE] tau <- c(0.05, 0.5, 0.95) set.seed(1) ## QRNN models w/ 2 hidden layers (tau=0.05, 0.50, 0.95) w <- p <- vector("list", length(tau)) for(i in seq_along(tau)){ w[[i]] <- qrnn2.fit(x=x, y=y, n.hidden=3, n.hidden2=3, tau=tau[i], iter.max=200, n.trials=1) p[[i]] <- qrnn2.predict(x, w[[i]]) } ## MCQRNN model w/ 2 hidden layers for simultaneous estimation of ## multiple non-crossing quantile functions x.y.tau <- composite.stack(x, y, tau) fit.mcqrnn <- qrnn2.fit(cbind(x.y.tau$tau, x.y.tau$x), x.y.tau$y, tau=x.y.tau$tau, n.hidden=3, n.hidden2=3, n.trials=1, iter.max=500, monotone=1) pred.mcqrnn <- matrix(qrnn2.predict(cbind(x.y.tau$tau, x.y.tau$x), fit.mcqrnn), ncol=length(tau)) par(mfrow=c(1, 2)) matplot(x, matrix(unlist(p), nrow=nrow(x), ncol=length(p)), col="red", type="l") points(x, y) matplot(x, pred.mcqrnn, col="blue", type="l") points(x, y)
dquantile gives a probability density function (pdf) by combining
step-interpolation of probability densities for specified
tau-quantiles (quant) with exponential lower/upper tails
(Quiñonero-Candela, 2006; Cannon, 2011). Point mass (e.g., as might occur
when using censored QRNN models) can be defined by setting lower to
the left censoring point. pquantile gives the cumulative distribution
function (cdf); the integrate function is used for values
outside the range of quant. The inverse cdf is given by
qquantile; the uniroot function is used for values
outside the range of tau. rquantile is used for
generating random variates.
Alternative formulations (without left censoring) based on the
Nadaraya-Watson estimator [p,q,r]quantile.nw are also provided
(Passow and Donner, 2020).
Note: these functions have not been extensively tested or optimized and should be considered experimental.
dquantile(x, tau, quant, lower=-Inf) pquantile(q, tau, quant, lower=-Inf, ...) pquantile.nw(q, tau, quant, h=0.001, ...) qquantile(p, tau, quant, lower=-Inf, tol=.Machine$double.eps^0.25, maxiter=1000, range.mult=1.1, max.error=100, ...) qquantile.nw(p, tau, quant, h=0.001) rquantile(n, tau, quant, lower=-Inf, tol=.Machine$double.eps^0.25, maxiter=1000, range.mult=1.1, max.error=100, ...) rquantile.nw(n, tau, quant, h=0.001)dquantile(x, tau, quant, lower=-Inf) pquantile(q, tau, quant, lower=-Inf, ...) pquantile.nw(q, tau, quant, h=0.001, ...) qquantile(p, tau, quant, lower=-Inf, tol=.Machine$double.eps^0.25, maxiter=1000, range.mult=1.1, max.error=100, ...) qquantile.nw(p, tau, quant, h=0.001) rquantile(n, tau, quant, lower=-Inf, tol=.Machine$double.eps^0.25, maxiter=1000, range.mult=1.1, max.error=100, ...) rquantile.nw(n, tau, quant, h=0.001)
x, q
|
vector of quantiles. |
p |
vector of cumulative probabilities. |
n |
number of random samples. |
tau |
ordered vector of cumulative probabilities associated with |
quant |
ordered vector of quantiles associated with |
lower |
left censoring point. |
tol |
tolerance passed to |
h |
bandwidth for Nadaraya-Watson kernel. |
maxiter |
maximum number of iterations passed to |
range.mult |
values of |
max.error |
maximum number of |
... |
dquantile gives the pdf, pquantile gives the cdf,
qquantile gives the inverse cdf (or quantile function), and
rquantile generates random deviates.
Cannon, A.J., 2011. Quantile regression neural networks: implementation in R and application to precipitation downscaling. Computers & Geosciences, 37: 1277-1284. doi:10.1016/j.cageo.2010.07.005
Passow, C., R.V. Donner, 2020. Regression-based distribution mapping for bias correction of climate model outputs using linear quantile regression. Stochastic Environmental Research and Risk Assessment, 34:87-102. doi:10.1007/s00477-019-01750-7
Quiñonero-Candela, J., C. Rasmussen, F. Sinz, O. Bousquet, B. Scholkopf, 2006. Evaluating Predictive Uncertainty Challenge. Lecture Notes in Artificial Intelligence, 3944: 1-27.
integrate, uniroot, qrnn.predict
## Normal distribution tau <- c(0.01, seq(0.05, 0.95, by=0.05), 0.99) quant <- qnorm(tau) x <- seq(-3, 3, length=500) plot(x, dnorm(x), type="l", col="red", lty=2, lwd=2, main="pdf") lines(x, dquantile(x, tau, quant), col="blue") q <- seq(-3, 3, length=20) plot(q, pnorm(q), type="b", col="red", lty=2, lwd=2, main="cdf") lines(q, pquantile(q, tau, quant), col="blue") abline(v=1.96, lty=2) abline(h=pnorm(1.96), lty=2) abline(h=pquantile(1.96, tau, quant), lty=3) abline(h=pquantile.nw(1.96, tau, quant, h=0.01), lty=3) p <- c(0.001, 0.01, 0.025, seq(0.05, 0.95, by=0.05), 0.975, 0.99, 0.999) plot(p, qnorm(p), type="b", col="red", lty=2, lwd=2, main="inverse cdf") lines(p, qquantile(p, tau, quant), col="blue") ## Distribution with point mass at zero tau.0 <- c(0.3, 0.5, 0.7, 0.8, 0.9) quant.0 <- c(0, 5, 7, 15, 20) r.0 <- rquantile(500, tau=tau.0, quant=quant.0, lower=0) x.0 <- seq(0, 40, by=0.5) d.0 <- dquantile(x.0, tau=tau.0, quant=quant.0, lower=0) p.0 <- pquantile(x.0, tau=tau.0, quant=quant.0, lower=0) q.0 <- qquantile(p.0, tau=tau.0, quant=quant.0, lower=0) par(mfrow=c(2, 2)) plot(r.0, pch=20, main="random") plot(x.0, d.0, type="b", col="red", main="pdf") plot(x.0, p.0, type="b", col="blue", ylim=c(0, 1), main="cdf") plot(p.0, q.0, type="b", col="green", xlim=c(0, 1), main="inverse cdf")## Normal distribution tau <- c(0.01, seq(0.05, 0.95, by=0.05), 0.99) quant <- qnorm(tau) x <- seq(-3, 3, length=500) plot(x, dnorm(x), type="l", col="red", lty=2, lwd=2, main="pdf") lines(x, dquantile(x, tau, quant), col="blue") q <- seq(-3, 3, length=20) plot(q, pnorm(q), type="b", col="red", lty=2, lwd=2, main="cdf") lines(q, pquantile(q, tau, quant), col="blue") abline(v=1.96, lty=2) abline(h=pnorm(1.96), lty=2) abline(h=pquantile(1.96, tau, quant), lty=3) abline(h=pquantile.nw(1.96, tau, quant, h=0.01), lty=3) p <- c(0.001, 0.01, 0.025, seq(0.05, 0.95, by=0.05), 0.975, 0.99, 0.999) plot(p, qnorm(p), type="b", col="red", lty=2, lwd=2, main="inverse cdf") lines(p, qquantile(p, tau, quant), col="blue") ## Distribution with point mass at zero tau.0 <- c(0.3, 0.5, 0.7, 0.8, 0.9) quant.0 <- c(0, 5, 7, 15, 20) r.0 <- rquantile(500, tau=tau.0, quant=quant.0, lower=0) x.0 <- seq(0, 40, by=0.5) d.0 <- dquantile(x.0, tau=tau.0, quant=quant.0, lower=0) p.0 <- pquantile(x.0, tau=tau.0, quant=quant.0, lower=0) q.0 <- qquantile(p.0, tau=tau.0, quant=quant.0, lower=0) par(mfrow=c(2, 2)) plot(r.0, pch=20, main="random") plot(x.0, d.0, type="b", col="red", main="pdf") plot(x.0, p.0, type="b", col="blue", ylim=c(0, 1), main="cdf") plot(p.0, q.0, type="b", col="green", xlim=c(0, 1), main="inverse cdf")
Tilted absolute value function. Also known as the check function, hinge function, or the pinball loss function.
tilted.abs(x, tau)tilted.abs(x, tau)
x |
numeric vector. |
tau |
desired tau-quantile. |
x <- seq(-2, 2, length=200) plot(x, tilted.abs(x, tau=0.75), type="l")x <- seq(-2, 2, length=200) plot(x, tilted.abs(x, tau=0.75), type="l")
The sigmoid, exponential linear elu, softplus,
lrelu, and relu functions can be used as the hidden layer
transfer function for a nonlinear QRNN model. sigmoid is
used by default. The linear function is used as the
hidden layer transfer function for linear QRNN models.
sigmoid.prime, elu.prime, softplus.prime,
lrelu.prime, relu.prime, and linear.prime
provide the corresponding derivatives.
sigmoid(x) sigmoid.prime(x) elu(x, alpha=1) elu.prime(x, alpha=1) softplus(x, alpha=2) softplus.prime(x, alpha=2) logistic(x) logistic.prime(x) lrelu(x) lrelu.prime(x) relu(x) relu.prime(x) linear(x) linear.prime(x)sigmoid(x) sigmoid.prime(x) elu(x, alpha=1) elu.prime(x, alpha=1) softplus(x, alpha=2) softplus.prime(x, alpha=2) logistic(x) logistic.prime(x) lrelu(x) lrelu.prime(x) relu(x) relu.prime(x) linear(x) linear.prime(x)
x |
numeric vector. |
alpha |
transition parameter for |
x <- seq(-10, 10, length=100) plot(x, sigmoid(x), type="l", col="black", ylab="") lines(x, sigmoid.prime(x), lty=2, col="black") lines(x, elu(x), col="red") lines(x, elu.prime(x), lty=2, col="red") lines(x, softplus(x), col="blue") lines(x, softplus.prime(x), lty=2, col="blue") lines(x, logistic(x), col="brown") lines(x, logistic.prime(x), lty=2, col="brown") lines(x, lrelu(x), col="orange") lines(x, lrelu.prime(x), lty=2, col="orange") lines(x, relu(x), col="pink") lines(x, relu.prime(x), lty=2, col="pink") lines(x, linear(x), col="green") lines(x, linear.prime(x), lty=2, col="green")x <- seq(-10, 10, length=100) plot(x, sigmoid(x), type="l", col="black", ylab="") lines(x, sigmoid.prime(x), lty=2, col="black") lines(x, elu(x), col="red") lines(x, elu.prime(x), lty=2, col="red") lines(x, softplus(x), col="blue") lines(x, softplus.prime(x), lty=2, col="blue") lines(x, logistic(x), col="brown") lines(x, logistic.prime(x), lty=2, col="brown") lines(x, lrelu(x), col="orange") lines(x, lrelu.prime(x), lty=2, col="orange") lines(x, relu(x), col="pink") lines(x, relu.prime(x), lty=2, col="pink") lines(x, linear(x), col="green") lines(x, linear.prime(x), lty=2, col="green")
Daily precipitation totals (mm) at Vancouver Int'l Airport (YVR) for the period 1971-2000.
Covariates for a simple downscaling task include daily sea-level pressures (Pa), 700-hPa specific humidities (kg/kg), and 500-hPa geopotential heights (m) from the NCEP/NCAR Reanalysis (Kalnay et al., 1996) grid point centered on 50 deg. N and 237.5 deg. E.
NCEP/NCAR Reanalysis data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA, from their Web site at https://psl.noaa.gov/.
Kalnay, E. et al., 1996. The NCEP/NCAR 40-year reanalysis project, Bulletin of the American Meteorological Society, 77: 437-470.
## YVR precipitation data with seasonal cycle and NCEP/NCAR Reanalysis ## covariates data(YVRprecip) y <- YVRprecip$precip x <- cbind(sin(2*pi*seq_along(y)/365.25), cos(2*pi*seq_along(y)/365.25), YVRprecip$ncep) ## Fit QRNN and quantile regression models for the conditional 75th ## percentile using the final 3 years of record for training and the ## remaining years for testing. train <- as.numeric(format(YVRprecip$date, "%Y")) >= 1998 test <- !train set.seed(1) w.qrnn <- qrnn.fit(x=x[train,], y=y[train,,drop=FALSE], n.hidden=1, tau=0.75, iter.max=200, n.trials=1, lower=0) p.qrnn <- qrnn.predict(x=x[test,], parms=w.qrnn) w.qreg <- qrnn.fit(x=x[train,], y=y[train,,drop=FALSE], tau=0.75, n.trials=1, lower=0, Th=linear, Th.prime=linear.prime) p.qreg <- qrnn.predict(x=x[test,], parms=w.qreg) ## Tilted absolute value cost function on test dataset qvs.qrnn <- mean(tilted.abs(y[test]-p.qrnn, 0.75)) qvs.qreg <- mean(tilted.abs(y[test]-p.qreg, 0.75)) cat("Cost QRNN", qvs.qrnn, "\n") cat("Cost QREG", qvs.qreg, "\n") ## Plot first year of test dataset plot(y[test][1:365], type="h", xlab="Day", ylab="Precip. (mm)") points(p.qrnn[1:365], col="red", pch=19) points(p.qreg[1:365], col="blue", pch=19)## YVR precipitation data with seasonal cycle and NCEP/NCAR Reanalysis ## covariates data(YVRprecip) y <- YVRprecip$precip x <- cbind(sin(2*pi*seq_along(y)/365.25), cos(2*pi*seq_along(y)/365.25), YVRprecip$ncep) ## Fit QRNN and quantile regression models for the conditional 75th ## percentile using the final 3 years of record for training and the ## remaining years for testing. train <- as.numeric(format(YVRprecip$date, "%Y")) >= 1998 test <- !train set.seed(1) w.qrnn <- qrnn.fit(x=x[train,], y=y[train,,drop=FALSE], n.hidden=1, tau=0.75, iter.max=200, n.trials=1, lower=0) p.qrnn <- qrnn.predict(x=x[test,], parms=w.qrnn) w.qreg <- qrnn.fit(x=x[train,], y=y[train,,drop=FALSE], tau=0.75, n.trials=1, lower=0, Th=linear, Th.prime=linear.prime) p.qreg <- qrnn.predict(x=x[test,], parms=w.qreg) ## Tilted absolute value cost function on test dataset qvs.qrnn <- mean(tilted.abs(y[test]-p.qrnn, 0.75)) qvs.qreg <- mean(tilted.abs(y[test]-p.qreg, 0.75)) cat("Cost QRNN", qvs.qrnn, "\n") cat("Cost QREG", qvs.qreg, "\n") ## Plot first year of test dataset plot(y[test][1:365], type="h", xlab="Day", ylab="Precip. (mm)") points(p.qrnn[1:365], col="red", pch=19) points(p.qreg[1:365], col="blue", pch=19)