cospi

Compute the cosine of the input real number multiplied by π.

Interface Definition

C interface:

float cospif(float x);

double cospi(double x);

Parameters

Parameter	Type	Description	Input/Output
x	For cospif, x is of single-precision floating-point type. For cospi, x is of double-precision floating-point type.	Floating-point value of the input data.	Input

Return Value

The cosine y of the input x multiplied by π is returned, that is, y = cos(x * π). y ∈ [-1, +1]
If the input is +0, the return value is 1.
If the input is -0, the return value is 1.
If the input is ±∞, the return value is NaN.
If the input is NaN, the return value is NaN.

Dependency

C: "km.h"

Example

C interface:

    // print result
    printf("cospi(0.0) = %.15f\n", cospi(0.0));
    printf("cospi(-0.0) = %.15f\n", cospi(-0.0));
    printf("cospi(0.25) = %.15f\n", cospi(0.25));
    printf("cospi(-0.25) = %.15f\n", cospi(-0.25));
    printf("cospi(0.5) = %.15f\n", cospi(0.5));
    printf("cospi(-0.5) = %.15f\n", cospi(-0.5));
    printf("cospi(1.0) = %.15f\n", cospi(1.0));
    printf("cospi(-1.0) = %.15f\n", cospi(-1.0));
    printf("cospi(2.0) = %.15f\n", cospi(2.0));
    printf("cospi(-2.0) = %.15f\n", cospi(-2.0));
    printf("cospi(INFINITY) = %.15f\n", cospi(INFINITY));
    printf("cospi(-INFINITY) = %.15f\n", cospi(-INFINITY));
    printf("cospi(NAN) = %.15f\n", cospi(NAN));
    printf("cospi(-NAN) = %.15f\n", cospi(-NAN));
    /* 
     * cospi(0.0) = 1.000000000000000
     * cospi(-0.0) = 1.000000000000000
     * cospi(0.25) = 0.707106781186548
     * cospi(-0.25) = 0.707106781186548
     * cospi(0.5) = 0.000000000000000
     * cospi(-0.5) = 0.000000000000000
     * cospi(1.0) = -1.000000000000000
     * cospi(-1.0) = -1.000000000000000
     * cospi(2.0) = 1.000000000000000
     * cospi(-2.0) = 1.000000000000000
     * cospi(INFINITY) = nan
     * cospi(-INFINITY) = nan
     * cospi(NAN) = nan
     * cospi(-NAN) = -nan
     * 
     * */

Parent topic: Trigonometric Functions