计算实数的余弦值。

接口定义

C interface:

float cosf(float x);

double cos(double x);

float complex ccosf(float complex x);

double complex ccos(double complex x);

Fortran interface:

RES = COSF(X);

RES = COS(X);

RES = CCOSF(X);

RES = CCOS(X);

参数

参数名	类型	描述	输入/输出
x	在cosf中，x是单精度浮点类型。在cos中，x是双精度浮点类型。在ccosf中，x是复数单精度浮点类型。在ccos中，x是复数双精度浮点类型。	表示弧度角的浮点值。	输入

返回值

返回弧度角x的余弦函数值y，y ∈ [-1, +1]。
输入+0，返回+1。
输入-0，返回+1。
输入±∞，返回nan。
输入nan，返回nan。

依赖

C: "km.h"

Fortran: "km.f03"

示例

C interface:

   double pi = acos(-1); 
    // typical usage 
    double a = pi/3, b = pi/2, c = -3*pi/4, d = 0.0; 
    // special handling 
    double e = INFINITY, f = -INFINITY, g = NAN; 
    double complex k = 0 + 0 * I;
    // print result 
    printf("cos(pi/3) = %.15f\n", cos(a)); 
    printf("cos(pi/2) = %.15f\n", cos(b)); 
    printf("cos(-3*pi/4) = %.15f\n", cos(c)); 
    printf("cos(0.0) = %.15f\n", cos(d)); 
    printf("cos(INFINITY) = %.15f\n", cos(e)); 
    printf("cos(-INFINITY) = %.15f\n", cos(f)); 
    printf("cos(NAN) = %.15f\n", cos(g)); 
    printf("ccos(0+0*I) = %.15f + %.15f * I\n", creal(ccos(k)), cimag(ccos(k)));
    /* 
     *  cos(pi/3) = 0.500000000000000 
     *  cos(pi/2) = 0.000000000000000 
     *  cos(-3*pi/4) = -0.707106781186547 
     *  cos(0.0) = 1.000000000000000 
     *  cos(INFINITY) = nan 
     *  cos(-INFINITY) = nan 
     *  cos(NAN) = nan 
     *  ccos(0+0*I) = 1 + -0 * I
     * 
     * */

Fortran interface:

    REAL(8) :: X = 0.0 
    PRINT*,  COS(X) 
    ! 
    ! OUTPUT 
    !     1.000000000000000 
    !