A vector with two components giving the range of the region on
which the Toy Signal is to be computed.
NPixel
Number of pixels of the result in one direction. The resulting
picture will have NPixel x NPixel pixels.
Value
A list with components "x", "y" and "z". Here, x and y are the
coordinates of the grid and z is matrix of dimensions
c(NPixel,NPixel) giving the Toy Signal.