---
title: atanpi
description: "计算输入实数的反正切值除以π。"
url: https://www.hikunpeng.com/document/detail/zh/kunpengaccel/math-lib/devg-kml/kunpengaccel_kml_0162.html
sourcePath: /source/zh/kunpengaccel/math-lib/devg-kml/kunpengaccel_kml_0162.html
indexId: 0fce3ca34ba4bce1440df4b3986f0a67f1452abd972722aebc2d3f6a82f401af68
---
# atanpi

计算输入实数的反正切值除以π。

#### 接口定义

C interface：

float atanpif(float x);

double atanpi(double x);


#### 参数

| 参数名 | 类型 | 描述 | 输入/输出 |
| --- | --- | --- | --- |
| x | 在atanpif中，x是单精度浮点类型。 在atanpi中，x是双精度浮点类型。 | 表示输入数据的浮点值。 | 输入 |


#### 返回值

- 正常区间：返回输入实数x的反正切函数值除以π的值y=atan(x) / π，y ∈ [-0.5, +0.5]。
- 特殊区间：如下所示。| 输入值（x） | 输出值（y） |
| --- | --- |
| +0 | +0 |
| \-0 | \-0 |
| +inf | 0.5 |
| \-inf | \-0.5 |
| nan | nan |


#### 依赖

C: "km.h"


#### 示例

C interface：```
// typical usage
float x1 = -1.0, x2 = 1.0, x3 = 0.5, x4 = -0.5;
// special handling
float a = 0.0, b = INFINITY, c = -INFINITY, d = NAN;
// print result
printf("atanpi(1.0) = %.15f\n", atanpi(x1));
printf("atanpi(-1.0) = %.15f\n", atanpi(x2));
printf("atanpi(0.5) = %.15f\n", atanpi(x3));
printf("atanpi(-0.5) = %.15f\n", atanpi(x4));
printf("atanpi(0.0) = %.15f\n", atanpi(a));
printf("atanpi(-0.0) = %.15f\n", atanpi(-a));
printf("atanpi(INFINITY) = %.15f\n", atanpi(b));
printf("atanpi(-INFINITY) = %.15f\n", atanpi(c));
printf("atanpi(NAN) = %.15f\n", atanpi(d));
/*
 *  atanpi(1.0) = -0.250000000000000
 *  atanpi(-1.0) = 0.250000000000000
 *  atanpi(0.5) = 0.147583617650433
 *  atanpi(-0.5) = -0.147583617650433
 *  atanpi(0.0) = 0.000000000000000
 *  atanpi(-0.0) = -0.000000000000000
 *  atanpi(INFINITY) = 0.500000000000000
 *  atanpi(-INFINITY) = -0.500000000000000
 *  atanpi(NAN) = nan
 *
 * */
```