zig/lib/std/math/complex/arg.zig

const std = @import("../../std.zig");
const testing = std.testing;
const math = std.math;
const cmath = math.complex;
const Complex = cmath.Complex;

/// Returns the angular component (in radians) of z.
pub fn arg(z: anytype) @TypeOf(z.re, z.im) {
    return math.atan2(z.im, z.re);
}

test arg {
    const epsilon = math.floatEps(f32);
    const a = Complex(f32).init(5, 3);
    const c = arg(a);
    try testing.expectApproxEqAbs(0.5404195, c, epsilon);
}