pow

Interface Definition

C interface:

float powf(float x, float y);

double pow(double x, double y);

Fortran interface:

RES = POWF(X, Y);

RES = POW(X, Y);

Parameters

Return Value

• If x is greater than 0 and y is a decimal, the result of x raised to the power of y is returned. The value range is r ∈ (-INF, +INF).
• If x is -0 and y is a negative odd number, the return value is -∞. If x is ±0 and y is a negative number, the return value is +∞.
• If x is ±0 and y is a positive odd number, the return value is ±0. If x is ±0, y is a positive number, the return value is +0.
• If x is ±1 and y is any value, the return value is +1.
• If x is any value and y is ±0, the return value is +1.
• If x is less than +0 and y is a decimal, the return value is NaN.
• If |x| is less than 1 and y is -∞, the return value is +∞. If |x| is greater than 1 and y is -∞, the return value is +0.
• If |x| is less than 1 and y is +∞, the return value is +0. If |x| is greater than 1 and y is +∞, the return value is +∞.
• If x is -∞ and y is a negative odd number, the return value is -0. If x is -∞ and y is a negative number, the return value is +0.
• If x is -∞ and y is a positive odd number, the return value is -∞. If x is -∞ and y is a positive number, the return value is +∞.
• If x is +∞ and y is less than +0, the return value is +0. If x is +∞ and y is greater than or equal to +0, the return value is +∞.
• If x and y are both large finite numbers, the return value is ±∞.
• If both x and y are NaN, the return value is NaN.

Dependencies

C: "km.h"

Fortran: "km.f03"

Examples

C interface:

    double pi = acos(-1); 
    // typical usage 
    double x1 = 1.0, x2 = 2.0, x3 = 3.0, x4 = 4.0;
    double y1 = 4.0, y2 = -4.0, y3 = -3.0, y4 = 3.0;
    // special handing 
    double a = 0.0, b = INFINITY, c = -INFINITY, d = NAN, e = 1.0; 
    // print result 
    printf("pow(1.0, 4.0) = %.15f\n", pow(x1, y1));
    printf("pow(2.0, -4.0) = %.15f\n", pow(x2, y2));
    printf("pow(3.0, -3.0) = %.15f\n", pow(x3, y3));
    printf("pow(4.0, 3.0) = %.15f\n", pow(x4, y4));
    printf("pow(1.0, 0.0) = %+.15f\n", pow(x1, a));
    printf("pow(INFINITY, 1.0) = %+.15f\n", pow(b, x1));
    printf("pow(-INFINITY, -1.0) = %+.15f\n", pow(c, -x1));
    printf("pow(1.0, -INFINITY) = %+.15f\n", pow(x1, c));
    printf("pow(1.0, NAN) = %+.15f\n", pow(x1, d));
    printf("pow(NAN, -1.0) = %+.15f\n", pow(d, -x1));
    /* 
     *  pow(1.0, 4.0) = 1.000000000000000
     *  pow(2.0, -4.0) = 0.062500000000000
     *  pow(3.0, -3.0) = 0.037037037037037
     *  pow(4.0, 3.0) = 64.000000000000000
     *  pow(1.0, 0.0) = +1.000000000000000
     *  pow(INFINITY, 1.0) = +inf
     *  pow(-INFINITY, -1.0) = -0.000000000000000
     *  pow(1.0, -INFINITY) = +1.000000000000000
     *  pow(1.0, NAN) = +1.000000000000000
     *  pow(NAN, -1.0) = +nan
     * 
     * */

    REAL(8) :: X = 3.0 
    REAL(8) :: Y = -3.0 
    PRINT*,  POW(X, Y) 
    ! 
    ! OUTPUT 
    !     0.037037037037037
    !