affine_rotation.hpp

#ifndef PASTELMATH_AFFINE_ROTATION_HPP
#define PASTELMATH_AFFINE_ROTATION_HPP

#include "pastel/math/affine/affine_rotation.h"

namespace Pastel
{

    template <typename Real>
    AffineTransformation<Real> affineRotation(
        integer n,
        integer i, integer j,
        const NoDeduction<Real>& angle)
    {
        PENSURE_OP(n, >=, 2);
        PENSURE_OP(i, >=, 0);
        PENSURE_OP(i, <, n);
        PENSURE_OP(j, >=, 0);
        PENSURE_OP(j, <, n);

        Real c = std::cos(angle);
        Real s = std::sin(angle);

        // For example, when
        // n = 2, i = 0, j = 1:
        //
        // [c -s]
        // [s  c]
        //
        // which is the counter-clockwise rotation
        // rotation of X to Y.
        //
        // If instead i = 1, and j = 0, then it is
        // the clockwise-rotation of Y to X.

        AffineTransformation<Real> result(n);

        result.matrix()(i, i) = c;
        result.matrix()(i, j) = -s;
        result.matrix()(j, i) = s;
        result.matrix()(j, j) = c;

        return result;
    }

}

#endif