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 matherr()               Handle Math Error

 #include   <math.h>

 int               matherr(x);
 struct exception  *x;                   Math exception information

    matherr() is called when errors are detected by the math functions.
    (See the individual math functions for specific information on when
    matherr() is called.)  A program can supply its own matherr()
    function to provide special error handling.

    When an error in a math function occurs, matherr() is called with a
    pointer to an exception structure, 'x', that holds the error
    information. The structure 'exception' is defined in math.h as:

          struct exception
                 {
                  int      type;        /* type of math error */
                  char     *name;       /* name of function causing error */
                  double   arg1, arg2;  /* argument(s) of math function */
                  double   retval;      /* default error return value */
                 };

    'type' specifies the type of math error and is one of the following
    values (defined in <math.h>):

                DOMAIN        Argument domain error
                SING          Argument singularity
                OVERFLOW      Overflow range error
                UNDERFLOW     Underflow range error
                TLOSS         Total loss of significance

    'name' is a pointer to a null-terminated string containing the name
    of the math function that caused the error; 'arg1' and 'arg2' (if the
    function accepts two arguments) are the argument(s) that caused the
    error; and 'retval' is the value that will be returned by the
    function for this error.  'retval' may be changed by matherr(), thus
    changing the value that will be returned by the math function. (Be
    careful:  The return value is used to specify that an error
    occurred.)

    matherr() returns 0 to indicate that an error still exists. In this
    case, the math function will print any error messages to 'stderr' and
    set 'errno' (defined in errno.h) to the appropriate error value.
    matherr() returns a non-zero value to indicate that the error has
    been corrected. In this case, the function should suppress error
    messages and should not set 'errno'.

       Returns:     0 to indicate that the error still exists and
                    non-zero to indicate that the error has been
                    corrected.

         Notes:     The default matherr() error handler just returns 0.

                    The following functions call matherr(): acos, asin,
                    atan, atan2, cabs, cos, cosh, exp, frexp, hypot,
                    ldexp, log, log10, pow, pow10, sin, sinh, sqrt, tan,
                    and tanh.