ACOSPI (The GNU Fortran Compiler)

### 8.9 `ACOSPI` — Circular arc cosine function ¶

Description:

  `ACOSPI(X)` computes \acos(x) / \pi, which is a measure of an angle in half-revolutions.

Standard:

  Fortran 2023

Class:

  Elemental function

Syntax:

  `RESULT = ACOSPI(X)`

Arguments:

  X | The type shall be `REAL` with -1 \leq x \leq 1.

Return value:

  The return value has the same type and kind as X. It is expressed in half-revolutions and satisfies 0 \leq \acospi (x) \leq 1.

Example:

      program test_acospi
        implicit none
        real, parameter :: x = 0.123, y(3) = [0.123, 0.45, 0.8]
        real, parameter :: a = acospi(x), b(3) = acospi(y)
        call foo(x, y)
      contains
        subroutine foo(u, v)
          real, intent(in) :: u, v(:)
          real :: f, g(size(v))
          f = acospi(u)
          g = acospi(v)
          if (abs(a - f) > 8 * epsilon(f)) stop 1
          if (any(abs(g - b) > 8 * epsilon(f))) stop 2
        end subroutine foo
      end program test_acospi

See also:

  `ASINPI` — Circular arc sine function
  `ATAN2PI` — Circular arc tangent function
  `ATANPI` — Circular arc tangent function