A demo of using Eigen3 as a vector arithmetic library

eigen-1.cpp

// https://eigen.tuxfamily.org/dox/GettingStarted.html
// https://eigen.tuxfamily.org/dox/group__TutorialMatrixArithmetic.html
//
// SeeAlso: https://www.boost.org/doc/libs/1_79_0/libs/qvm/doc/html/index.html

#define EIGEN_INITIALIZE_MATRICES_BY_ZERO

#include <iostream>
#include <Eigen/Dense>

int main()
{
        using namespace Eigen;
        using namespace std;

        // Vector3 is a 3x1 matrix

        IOFormat vec(
                StreamPrecision,        // precision: use iostream settings
                0,                      // flags
                "",                     // coeffSeparator
                ",",                    // rowSeparator:
                                        //         no need to add spaces here
                                        //         because Eigen will use the 'fill' argument (defaults to ' ')
                                        //         to "fill the empty space in aligned columns"
                "",                     // rowPrefix
                "",                     // rowSuffix
                "(",                    // matPrefix
                ")");                   // matSuffix


        Vector3d u(1, 2, 3);
        Vector3d v(0, 2, 1);

        cout << "---\n";
        cout << u << '\n';

        cout << "---\n";
        cout << u.format(vec) << '\n';
        cout << v.format(vec) << '\n';

        cout << "---\n";
        cout << "                    add: " << (u + v).format(vec) << '\n';
        cout << "               subtract: " << (u - v).format(vec) << '\n';
        cout << "component-wise multiply: " << u.cwiseProduct(v).format(vec) << '\n';
        cout << "             left scale: " << (7 * u).format(vec) << '\n';
        cout << "            right scale: " << (u * 7).format(vec) << '\n';
        cout << "                 negate: " << (-u).format(vec) << '\n';
        cout << "            dot product: " << u.dot(v) << '\n';
        cout << "          cross product: " << u.cross(v).format(vec) << '\n';
        cout << "                 length: " << u.norm() << '\n';                          // sqrt(14)
        cout << "              normalize: " << u.normalized().format(vec) << '\n';
        cout << "              equals[1]: " << (u == u) << '\n';
        cout << "              equals[2]: " << (u == v) << '\n';

        cout << "---\n";
        cout << "x: " << u.x() << '\n';
        cout << "y: " << u.y() << '\n';
        cout << "z: " << u.z() << '\n';

        cout << "---\n";
        cout << "zero: " << Vector3d().format(vec) << '\n';                     // EIGEN_INITIALIZE_MATRICES_BY_ZERO

        cout << "---\n";
        cout << "swizzle:\n";
        cout << " xy: " << u({0, 1}).format(vec) << '\n';
        cout << " yz: " << u({1, 2}).format(vec) << '\n';
        cout << " zx: " << u({2, 0}).format(vec) << '\n';
        cout << " yy: " << u({1, 1}).format(vec) << '\n';
        cout << "zyx: " << u({2, 1, 0}).format(vec) << '\n';

        return 0;
}