atan2

接口定义

C interface：

float atan2f(float y, float x);

double atan2(double y, double x);

long double atan2l(long double y, long double x);

Fortran interface：

RES = ATAN2F(Y,X);

RES = ATAN2(Y,X);

参数

返回值

对于atan2(y, x)来说，返回的是原点至点(x, y)的方位角，即与x轴的夹角。返回值的单位为弧度，取值范围为(-π, +π]。

• 输入y为±0，x为负或-0，则返回±π。
• 输入y为±0，x为正或+0，则返回±0。
• 输入y为±∞，x为有限，则返回±π/2。
• 输入y为±∞，x为-∞，则返回±3π/4。
• 输入y为±∞，x为+∞，则返回±π/4。
• 输入x为±0，y为负，则返回-π/2。
• 输入x为±0，y为正，则返回+π/2。
• 输入x是-∞，y是有限且正的，则返回+π。
• 输入x为-∞，y为有限负，则返回-π。
• 输入x为+∞，且y为有限且为正，则返回+0。
• 输入x为+∞，且y为有限且为负，则返回-0。
• 输入x为nan，或y为nan，则返回nan。

依赖

C: "km.h"

示例

C interface：

    double pi = acos(-1); 
    // typical usage 
    double x1 = 1.0, y1 = pi/2, x2 = -3*pi/4, y2 = 2.0; 
    double x3 = 4.0, y3 = -4.0, x4 = -3.0, y4 = 3.0; 
    // special handling 
    double a = 0.0, b = INFINITY, c = -INFINITY, d = NAN; 
    // print result 
    printf("atan2(pi/2, 1.0) = %.15f\n", atan2(y1, x1)); 
    printf("atan2(2.0, -3*pi/4) = %.15f\n", atan2(y2, x2)); 
    printf("atan2(-4.0, 4.0) = %.15f\n", atan2(y3, x3)); 
    printf("atan2(3.0, -3.0) = %.15f\n", atan2(y4, x4)); 
    printf("atan2(+0.0, +0.0) = %+.15f\n", atan2(a, a)); 
    printf("atan2(+0.0, -0.0) = %+.15f\n", atan2(a, -a)); 
    printf("atan2(-0.0, +0.0) = %+.15f\n", atan2(-a, a)); 
    printf("atan2(-0.0, -0.0) = %+.15f\n", atan2(-a, -a)); 
    printf("atan2(+0.0, -4.0) = %+.15f\n", atan2(a, y3)); 
    printf("atan2(-0.0, +3.0) = %+.15f\n", atan2(-a, y4)); 
    printf("atan2(-4.0, +0.0) = %+.15f\n", atan2(y3, a)); 
    printf("atan2(+3.0, -0.0) = %+.15f\n", atan2(y4, -a)); 
    printf("atan2(INFINITY, 1.0) = %+.15f\n", atan2(b, x1)); 
    printf("atan2(-INFINITY, -1.0) = %+.15f\n", atan2(c, -x1)); 
    printf("atan2(1.0, -INFINITY) = %+.15f\n", atan2(x1, c)); 
    printf("atan2(-3.0, -INFINITY) = %+.15f\n", atan2(x4, c)); 
    printf("atan2(1.0, INFINITY) = %+.15f\n", atan2(x1, b)); 
    printf("atan2(-3.0, INFINITY) = %+.15f\n", atan2(x4, b)); 
    printf("atan2(1.0, NAN) = %+.15f\n", atan2(x1, d)); 
    printf("atan2(NAN, -1.0) = %+.15f\n", atan2(d, -x1)); 
    /* 
     *  atan2(pi/2, 1.0) = 1.003884821853887 
     *  atan2(2.0, -3*pi/4) = 2.437780340738381 
     *  atan2(-4.0, 4.0) = -0.785398163397448 
     *  atan2(3.0, -3.0) = 2.356194490192345 
     *  atan2(+0.0, +0.0) = +1.570796326794897 
     *  atan2(+0.0, -0.0) = +1.570796326794897 
     *  atan2(-0.0, +0.0) = +1.570796326794897 
     *  atan2(-0.0, -0.0) = +1.570796326794897 
     *  atan2(+0.0, -4.0) = +3.141592653589793 
     *  atan2(-0.0, +3.0) = +0.000000000000000 
     *  atan2(-4.0, +0.0) = -1.570796326794897 
     *  atan2(+3.0, -0.0) = +1.570796326794897 
     *  atan2(INFINITY, 1.0) = +1.570796326794897 
     *  atan2(INFINITY, -1.0) = -1.570796326794897 
     *  atan2(1.0, -INFINITY) = +3.141592653589793 
     *  atan2(-3.0, -INFINITY) = -3.141592653589793 
     *  atan2(1.0, INFINITY) = +0.000000000000000 
     *  atan2(-3.0, INFINITY) = -0.000000000000000 
     *  atan2(1.0, NAN) = +nan 
     *  atan2(NAN, -1.0) = +nan 
     * 
     * */

Fortran interface：

    REAL(8) :: X = 3.0 
    REAL(8) :: Y = -3.0 
    PRINT*,  ATAN2(Y, X) 
    ! 
    ! OUTPUT 
    !     2.356194490192345 
    !