ACOSH(3)

NAME
1.4 `acosh', `acoshf'--inverse hyperbolic cosine

SYNOPSIS
     #include <math.h>
     double acosh(double X);
     float acoshf(float X);

DESCRIPTION
`acosh' calculates the inverse hyperbolic cosine of X. `acosh' is defined as
      log(X + sqrt(X*X-1))
   X must be a number greater than or equal to 1.
   `acoshf' is identical, other than taking and returning floats.

RETURNS
`acosh' and `acoshf' return the calculated value. If X less than 1, the return value is NaN and `errno' is set to `EDOM'.
   You can change the error-handling behavior with the non-ANSI `matherr' function.

PORTABILITY
Neither `acosh' nor `acoshf' are ANSI C. They are not recommended for portable programs.

SEE ALSO
acosh is part of the library. The full documentation for is maintained as a Texinfo manual. If info and are properly installed at your site, the command

    info

will give you access to the complete manual.