topic Re: Do until loop in SAS/IML Software and Matrix Computations

Do until loop

Ioana — Thu, 03 Oct 2013 16:43:09 GMT

Hello,

I am new to SAS and I would like to know how to tweak this program to break the infinite do until loop. At the end of the do until loop I would like to be able to print the updated phi. Thanks.

Re: Do until loop

Astounding — Thu, 03 Oct 2013 17:24:28 GMT

With any DO UNTIL loop, it is possible that it never ends because the UNTIL condition never becomes true. In your case, this condition might never become true: (n < 0.001)

One way to guard against it is to allow two ways for the loop to end:

do k=1 to 100000 until (n < 0.001);

If the loop iterates 100,000 times, it will end regardless of the value of n. Your subsequent statements might have to allow for the possibility that n > 0.001. The loop will end before 100,000 iterations if the UNTIL condition becomes true.

Good luck.

Re: Do until loop

Rick_SAS — Thu, 03 Oct 2013 17:33:35 GMT

Welcome to SAS! To break the infinite DO UNTIL loop, I often include a maximum number of iterations, like this:

maxIter = 50;

iter = 0;

do until(n<0.001 | iter>=maxIter);

/* computations */

n = sqrt(direc[##]);

iter = iter + 1;

end;

If I might offer another suggestion, your computation is looping over the I variable 50,000 times and updating elements of vectors. It might be possible for you to eliminate that loop. For ideas, see

http://blogs.sas.com/content/iml/2013/05/15/vectorize-computations/

Re: Do until loop

Ioana — Fri, 04 Oct 2013 01:17:14 GMT

Thank you so much.

Re: Do until loop

Ioana — Fri, 04 Oct 2013 01:18:11 GMT

Thank you so much.