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An Introductory SAS/IML Program

This section presents a simple introductory SAS/IML program that implements a numerical algorithm that estimates the square root of a number, accurate to three decimal places. The following statements define a function module named MySqrt that performs the calculations:

proc iml;                   /* begin IML session */

start MySqrt(x);            /* begin module */
   y = 1;                   /* initialize y */
   do until(w<1e-3);        /* begin DO loop */
      z = y;                /* set z=y */
      y = .5#(z+x/z);       /* estimate square root */
      w = abs(y-z);         /* compute change in estimate */
   end;                     /* end DO loop */
   return(y);               /* return approximation */
finish;                     /* end module */

You can call the MySqrt module to estimate the square root of several numbers given in a matrix literal (enclosed in braces) and print the results:

t = MySqrt({3,4,7,9});      /* call function MySqrt  */
s = sqrt({3,4,7,9});        /* compare with true values */
diff = t - s;               /* compute differences */
print t s diff;             /* print matrices */

Figure 2.1 Approximate Square Roots

t	s	diff
1.7320508	1.7320508	0
2	2	2.22E-15
2.6457513	2.6457513	4.678E-11
3	3	1.397E-9