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`sqrt', `sqrtf'--positive square root

     #include <math.h>
     double sqrt(double X);
     float  sqrtf(float X);
`sqrt' computes the positive square root of the argument.  You can
modify error handling for this function with `matherr'.
On success, the square root is returned. If X is real and positive,
then the result is positive.  If X is real and negative, the global
value `errno' is set to `EDOM' (domain error).
`sqrt' is ANSI C.  `sqrtf' is an extension.