R Under development (unstable) (2023-10-23 r85401 ucrt) -- "Unsuffered Consequences"
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> # tgrchk.R -- test gradient check for bad inputs or calls
> ##  author: John C. Nash
> # rm(list=ls())
> cat("Show how grchk works\n")
Show how grchk works
> require(optimx)
Loading required package: optimx
> 
> jones<-function(xx){
+   x<-xx[1]
+   y<-xx[2]
+   ff<-sin(x*x/2 - y*y/4)*cos(2*x-exp(y))
+   ff<- -ff
+ }
> 
> jonesg <- function(xx) {
+   x<-xx[1]
+   y<-xx[2]
+   gx <-  cos(x * x/2 - y * y/4) * ((x + x)/2) * cos(2 * x - exp(y)) - 
+     sin(x * x/2 - y * y/4) * (sin(2 * x - exp(y)) * 2)
+   gy <- sin(x * x/2 - y * y/4) * (sin(2 * x - exp(y)) * exp(y)) - cos(x * 
+                                                                         x/2 - y * y/4) * ((y + y)/4) * cos(2 * x - exp(y))
+   gg <- - c(gx, gy)
+ }
> 
> xx <- c(1, 2)
> 
> gcans <- grchk(xx, jones, jonesg, trace=1, testtol=(.Machine$double.eps)^(1/3))
gradient test tolerance =  6.055454e-06   fval= 0.3002153 
 compare to max(abs(gn-ga))/(1+abs(fval)) =  1.312852e-11 
> gcans
[1] TRUE
attr(,"ga")
[1] -1.297122  3.311502
attr(,"gn")
[1] -1.297122  3.311502
attr(,"maxdiff")
[1] 1.70699e-11
> 
> 
> 
> proc.time()
   user  system elapsed 
   0.20    0.03    0.21