File:Bvn-small.png

Summary
I made this file in the R programming language using the following code:

myseq<-seq(-3,3,length=100) mygrid<-expand.grid(x1=myseq,x2=myseq) mygrid$y<-dnorm(mygrid$x1)*dnorm(mygrid$x2) require(lattice) png(file="bvn.png", height = 450, width = 1100) print(wireframe(y~x1*x2, data=mygrid, shade=TRUE, scales=list(arrows=FALSE,                            x=list(draw=FALSE),                             y=list(draw=FALSE),                             z=list(draw=FALSE)                             ), aspect=c(1,1/3), xlab="", ylab="", zlab="", par.box = list(col=NA))      ) dev.off

followed by some manipulations in The GIMP.