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 sqrt()                  Calculate Square Root

 #include   <math.h>

 double     sqrt(x);
 double     x;                           Non-negative floating-point value

    sqrt() returns the square root of 'x'.  'x' must be a non-negative,
    floating-point number.

    Returns:    Square root of 'x'.  If 'x' is negative, matherr() is
                called with a DOMAIN error, a DOMAIN error message is
                printed to 'stderr', 'errno' (defined in <stdlib.h>) is
                set to EDOM (defined in <math.h>), and 0.0 is returned.

      Notes:    Error handling can be modified with the matherr()
                routine.

   -------------------------------- Example ---------------------------------

    The following statements calculate the square root of 25.0, 0.0, and
    -4.0 (-4.0 causes an error):

           #include <math.h>       /* for sqrt() and EDOM */
           #include <stdio.h>      /* for printf() */
           #include <stdlib.h>     /* for errno */

           main()
           {
               double a, b, c;

               a = sqrt(25.0);    /* a = 5.0 */
               b = sqrt(0.0);     /* b = 0.0 */
               errno = 0;
               c = sqrt(-4.0);    /* c = 0.0, causes EDOM error */
               if (errno == EDOM)
                   printf("EDOM error in sqrt()\n");
           }