---
title: y0
description: "Bessel 0阶第二类函数，x > 0。"
url: https://www.hikunpeng.com/document/detail/zh/kunpengboostkithistory/2300/accel/kunpengaccel_kml_16_0683.html
sourcePath: /source/zh/kunpengboostkithistory/2300/accel/kunpengaccel_kml_16_0683.html
indexId: 58b9707e9cc961f4cebe3655800f7dd3968ebd348bb4228af9e47b512620b50c74
---
# y0

Bessel 0阶第二类函数，x > 0。

#### 接口定义

C interface：

float y0f(float x);

double y0(double x);


#### 参数

| 参数名 | 类型 | 描述 | 输入/输出 |
| --- | --- | --- | --- |
| x | 在y0f中，x是单精度浮点类型。 在y0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

- 返回以0阶第二类贝塞尔函数值y，y ∈ (-∞, +1)。
- 输入x为±0，返回-∞。
- 输入x<0，返回nan。
- 输入x为+∞，返回0。
- 输入x为nan，返回nan。


#### 依赖

C: "km.h"


#### 示例

C interface：

```
double x1 = 0.0, x2 = -0.0, x3 = 1.5, x4 = -2.5;
// special handing
double a = INFINITY, b = -INFINITY, c = NAN;
// print result
printf("y0(0.0) = %.15f\n", y0(x1));
printf("y0(-0.0) = %.15f\n", y0(x2));
printf("y0(1.5) = %.15f\n", y0(x3));
printf("y0(-2.5) = %.15f\n", y0(x4));
printf("y0(INFINITY) = %.15f\n", y0(a));
printf("y0(-INFINITY) = %.15f\n", y0(b));
printf("y0(NAN) = %.15f\n", y0(c));
/*
* y0(0.0) = -inf
* y0(-0.0) = -inf
* y0(1.5) = 0.382448923797759
* y0(-2.5) = nan
* y0(INFINITY) = 0.000000000000000
* y0(-INFINITY) = nan
* y0(NAN) = nan
*
* */
```