Hi Rainman, Are you thinking on the following algorithm?: http://en.wikipedia.org/wiki/Scale-in... IDL does not come with it. We can certainly added to a Feature Request. I think at the moment you will need to write it yourself. Apologies about this, I hope it's not a very complicated algorithm. Regards, Fernando

yes, I want to do it. I write it by C, then call the 'exe'. Now I have another question: how to get the Moore-Penrose inverse ? I use 'IMSL_CHNNDSOL', but it didn't work. my matrix: [x1,y1,1,0,0,0 0,0,0,x2,y2,1 ..... 0,0,0,xn,yn,1]

Hi Rainman, Are you thinking about the following: http://en.wikipedia.org/w...enrose_pseudoinverse I'm afraid that IDL doesn't have a routine to do that. Why would you like to use IMSL_CHNNDSOL for that? Cheers, fernando