Date:         Mon, 21 Jan 2008 09:55:17 -0500
Reply-To:     "Richard A. DeVenezia" <rdevenezia@WILDBLUE.NET>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         "Richard A. DeVenezia" <rdevenezia@WILDBLUE.NET>
Organization: Internet News Service
Subject:      Re: Largest value in a symmetric matrix
Comments: To: sas-l@uga.edu

Stefan Pohl wrote:
> Hi SAS-group,
>
> I want to know which is the largest value in the following matrix
>
> id  var1 var2 var3 var4
> 1   0    1    2    1
> 2   1    0    5    4
> 3   2    5    0    3
> 4   1    4    3    0
>
> the matrix is symmetric
>
> How can I do this?

You can use the MAX function and a retained variable.

------
data _null_;
    retain maxvalue;

    set MyData end=end;
    maxvalue = max (maxvalue, of var1-var4);

    if end then call symputx('maxvalue',maxvalue);
run;

------
The issue of symmetry does not come into play.  A more complex looping
approach that is symmetry aware could perform 1/2 the number of comparisons
to arrive at the answer.  This does not mean it would always take less
time -- the MAX function might be able to loop faster internally than some
externally managed loop.

--
Richard A. DeVenezia
http://www.devenezia.com/