---
title: cproj
description: "计算复数在黎曼球面的投影。"
url: https://www.hikunpeng.com/document/detail/zh/kunpenghpcs/hpckit/devg/kunpengaccel_kml_0279.html
sourcePath: /source/zh/kunpenghpcs/hpckit/devg/kunpengaccel_kml_0279.html
indexId: 594317a0edae6963cd422c895d4eedcf1244aa527667b1caa75441b4749d256061
---
# cproj

计算复数在黎曼球面的投影。

#### 接口定义

C interface：

float complex cprojf(float complex x);

double complex cproj(double complex x);

long double complex cprojl(long double complex x);


#### 参数

| 参数名 | 类型 | 描述 | 输入/输出 |
| --- | --- | --- | --- |
| x | 在cprojf中，x是复数单精度浮点类型。 在cproj中，x是复数双精度浮点类型。 在cprojl中，x是复数长双精度浮点类型。 | 表示输入数据的浮点值。 | 输入 |


#### 返回值

- 返回x在黎曼球面的投影y。
- 输入x.real或者x.imag为±∞，返回y.real为+∞，y.imag为0（y.imag符号和x.imag一致）。
- 输入x.real和x.imag均不为±∞，y=x。


#### 依赖

C: "kc.h"


#### 示例

C interface：```
// typical usage
    double x1 = INFINITY, y1 = INFINITY;
    double x2 = 2.0, y2 = 3.0;
    double x3 = -2.5, y3 = -3.4;
    double x4 = NAN, y4 = NAN;
    double x5 = 0, y5 = 0;
    double complex z1 = cproj(__builtin_complex(x1, y1));
    double complex z2 = cproj(__builtin_complex(x2, y2));
    double complex z3 = cproj(__builtin_complex(x3, y3));
    double complex z4 = cproj(__builtin_complex(x4, y4));
    double complex z5 = cproj(__builtin_complex(x5, y5));
    // print result
    printf("/*\n");
    printf(" * cproj(%.2f + %.2f*I) = %.6f + %.6f*I\n", x1, y1, __real__(z1), __imag__(z1));
    printf(" * cproj(%.2f + %.2f*I) = %.6f + %.6f*I\n", x2, y2, __real__(z2), __imag__(z2));
    printf(" * cproj(%.2f + %.2f*I) = %.6f + %.6f*I\n", x3, y3, __real__(z3), __imag__(z3));
    printf(" * cproj(%.2f + %.2f*I) = %.6f + %.6f*I\n", x4, y4, __real__(z4), __imag__(z4));
    printf(" * cproj(%.2f + %.2f*I) = %.6f + %.6f*I\n", x5, y5, __real__(z5), __imag__(z5));
    printf(" **/\n");
 
   /*
    * cproj(inf + inf*I) = inf + 0.000000*I
    * cproj(2.00 + 3.00*I) = 2.000000 + 3.000000*I
    * cproj(-2.50 + -3.40*I) = -2.500000 + -3.400000*I
    * cproj(nan + nan*I) = nan + nan*I
    * cproj(0.00 + 0.00*I) = 0.000000 + 0.000000*I
    **/
```