vector_cross_product.cpp

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#include <array>
#include <cassert>
#include <cmath>

namespace math {
namespace vector_cross {
std::array<double, 3> cross(const std::array<double, 3> &A,
                            const std::array<double, 3> &B) {
    std::array<double, 3> product;
    product[0] = (A[1] * B[2]) - (A[2] * B[1]);
    product[1] = -((A[0] * B[2]) - (A[2] * B[0]));
    product[2] = (A[0] * B[1]) - (A[1] * B[0]);
    return product;
}

double mag(const std::array<double, 3> &vec) {
    double magnitude =
        sqrt((vec[0] * vec[0]) + (vec[1] * vec[1]) + (vec[2] * vec[2]));
    return magnitude;
}
}  // namespace vector_cross
}  // namespace math

static void test() {
    std::array<double, 3> t_vec =
        math::vector_cross::cross({1, 2, 3}, {4, 5, 6});
    assert(t_vec[0] == -3 && t_vec[1] == 6 && t_vec[2] == -3);

    double t_mag = math::vector_cross::mag({6, 8, 0});
    assert(t_mag == 10);

    std::array<double, 3> t_vec2 =
        math::vector_cross::cross({1, 2, 3}, {1, 2, 3});
    assert(t_vec2[0] == 0 && t_vec2[1] == 0 &&
           t_vec2[2] == 0);  // checking each element
    assert(math::vector_cross::mag(t_vec2) ==
           0);  // checking the magnitude is also zero
}

int main() {
    test();
    return 0;
}