Auto-suggest helps you quickly narrow down your search results by suggesting possible matches as you type.

Showing results for

- RSS Feed
- Mark Topic as New
- Mark Topic as Read
- Float this Topic for Current User
- Bookmark
- Subscribe
- Mute
- Printer Friendly Page

- Mark as New
- Bookmark
- Subscribe
- Mute
- RSS Feed
- Permalink
- Report Inappropriate Content

Posted 04-28-2012 11:43 AM
(1473 views)

I'm trying to pull the lower half of a matrix in proc iml. It seems like the VECH function would work perfectly, but I'm running SAS 9.2 and VECH appears to be limited to 9.3. Any suggestions for alternatives? It's all inside a loop and the matrix size changes (with each loop), but these are fairly large matrices (e.g., 3000 X 3000). Thanks!

4 REPLIES 4

- Mark as New
- Bookmark
- Subscribe
- Mute
- RSS Feed
- Permalink
- Report Inappropriate Content

This can be recreated using a short function module, but it is complicated slightly by the fact that the LOC function operates in row major order while the VECH function operates in column major order, and so the need to transpose the matrix. The code below should do the trick, but I have no idea how efficient or inefficient this might be with your large matrices.

proc iml;

start vechalf(x);

a=nrow(x);

b=a#a-1;

return(t(x)[loc(mod(0:b,a)>=int((0:b)/a))]);

finish;

x=shape(10:25,4,4);

print x;

y=vechalf(x);

print y;

quit;

- Mark as New
- Bookmark
- Subscribe
- Mute
- RSS Feed
- Permalink
- Report Inappropriate Content

Actually it appears the symsqr function did what i needed.

thanks,

Rick

- Mark as New
- Bookmark
- Subscribe
- Mute
- RSS Feed
- Permalink
- Report Inappropriate Content

Thanks for the info, I had read this article and come to the conclusion that VECH was something completely new, but it appears that SYMSQR does the same thing, only it reads the lower diagonal elements in row-major order, so the two do give different results. It would be nice if the 9.3 documentation for VECH could be changed to include a link to SYMSQR (and vice versa).

Ian.

- Mark as New
- Bookmark
- Subscribe
- Mute
- RSS Feed
- Permalink
- Report Inappropriate Content

Are you ready for the spotlight? We're accepting content ideas for **SAS Innovate 2025** to be held May 6-9 in Orlando, FL. The call is **open **until September 25. Read more here about **why** you should contribute and **what is in it** for you!

Multiple Linear Regression in SAS

Learn how to run multiple linear regression models with and without interactions, presented by SAS user Alex Chaplin.

Find more tutorials on the SAS Users YouTube channel.