---
title: cos
description: "计算实数的余弦值。"
url: https://www.hikunpeng.com/document/detail/zh/kunpengboostkithistory/220RC3/accel/kunpengaccel_kml_16_0114.html
sourcePath: /source/zh/kunpengboostkithistory/220RC3/accel/kunpengaccel_kml_16_0114.html
indexId: 41e2610a1668b1b11e3f26406ae8bd48983c333a5fb90ac65cf105612450669876
---
# cos

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
!
```