Ondrej

I am not sure, but there might be potential bugs in case a=0.

If a=0, code jumps to the end, at tries to evaluate variable "e"..which does not exist.
Also, as far as I know, case a=0, b=1, corresponds to sum of geometric progression (1/(1-z)), therefore a=0, should be allowed in the code.

What about adding a next optional parameter which would set the "darkness/lightness", such that the mapping between color and grayscale wouldn't be linear.
Easy way how to do is to add a line, e.g.
RGBmap = brighten(RGBmap,0.2)
The problem is, however, that the mapping is not smooth (as can be seen on the plot, if I do e.g. colorGray(100,1)).

I don't quite understand what kind of problem you had, Muhammad. The function should return normal adjacency matrix and not adjacency list. Could you please provide some example and the expected result you would want? And of course, if you noticed some incorrect behaviour, I would gladly fix it.

Oops! Forget my latter question :-)

I just uploaded an updated version with self-loops checks and I also added an example. However, I left the conversion to sparse matrix unchanged, because I believe that in most cases the adjency matrix will contain "enough" zeros to have the computation more efficient.
btw. I didn't use spdiags because according to my simulations, it is slower than normal diag (and since I use it only for a check, it shouldn't last long).

P.S. Thank you once again Wolfgang for all those hints.