The following data set and macro variables contain the input data that are used in this example:

data a_data;
   input a @@;
   datalines;
9 13 -14 17 13 -19 23 21
;

%let b = 37;

/* populate macro variable n as number of decision variables */
%let dsid = %sysfunc(open(a_data));
%let n = %sysfunc(attrn(&dsid, NOBS));
%let rc = %sysfunc(close(&dsid));