tan

tan

Compute the Trigonometric Tangent

Portability: ISO/ANSI C conforming, UNIX compatible

SYNOPSIS
DESCRIPTION
RETURN VALUE
DIAGNOSTICS
EXAMPLE
RELATED FUNCTIONS
SEE ALSO

SYNOPSIS

#include <math.h>

double tan(double x);

DESCRIPTION

tan computes the trigonometric tangent of an argument x expressed in radians.

Because the tangent function is periodic, only the value of x mod 2 [pi] is used to compute the tangent. If x is very large, only a limited precision is left to represent x mod 2 [pi] . Thus, an error message is written for very large negative or positive arguments (see DIAGNOSTICS).

RETURN VALUE

tan returns the value of the tangent of the argument x , provided that this value is defined and computable. The return value is a double-precision, floating-point number.

DIAGNOSTICS

The tangent is not defined if x is ± [pi] /2, ± 3 [pi] /2, or any other value of the following form:

[pi]/2 + n[pi]

n is an integer.

If the value of x is so close to an odd multiple of [pi] /2 that the tangent cannot be represented accurately, the function returns HUGE_VAL . The run-time library writes an error message to stderr (the standard error file).

If the value of x is greater than 6.7465e9, the function returns 0.0. In this case, the message "total loss of significance" is also written to stderr .

If an error occurs in tan , the _matherr routine is called. You can supply your own version of _matherr to suppress the diagnostic message or modify the value returned.

EXAMPLE

#include <stdio.h>
#include <math.h>

#define YVAL 1.04

main()
{
   double cotan;

      /* The cotangent is 1 divided by the */
      /*  tangent of YVAL.                 */
   cotan = 1 / tan(YVAL);
   printf("1 / tan(%f) = %f\n", YVAL, cotan);
}

RELATED FUNCTIONS

cos , _matherr , sin

SEE ALSO

Mathematical Functions

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