8.80 COSPI — Circular cosine function

Description:

COSPI(X) computes \cos(\pi x) without performing an explicit multiplication by \pi. This is achieved through argument reduction where x = n + r with n an integer and 0 \leq r \le 1. Due to the properties of floating-point arithmetic, the useful range for X is defined by ABS(X) <= REAL(2,KIND(X))**DIGITS(X).

Standard:

Fortran 2023

Class:

Elemental function

Syntax:

RESULT = COSPI(X)

Arguments:
XThe type shall be REAL.
Return value:

The return value is of the same type and kind as X. The result is in half-revolutions and satisfies -1 \leq \cospi (x) \leq 1.

Example:
program test_cospi
  real :: x = 0.0
  x = cospi(x)
end program test_cospi
See also:

ACOSPI — Circular arc cosine function
COS — Cosine function