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function rotmat = quat2rotmat(qvec)

rotmat = [1 - 2 * qvec(3).^2 - 2 * qvec(4).^2, ...
          2 * qvec(2) * qvec(3) - 2 * qvec(1) * qvec(4), ...
          2 * qvec(4) * qvec(2) + 2 * qvec(1) * qvec(3); ...

          2 * qvec(2) * qvec(3) + 2 * qvec(1) * qvec(4), ...
          1 - 2 * qvec(2).^2 - 2 * qvec(4).^2, ...
          2 * qvec(3) * qvec(4) - 2 * qvec(1) * qvec(2); ...

          2 * qvec(4) * qvec(2) - 2 * qvec(1) * qvec(3), ...
          2 * qvec(3) * qvec(4) + 2 * qvec(1) * qvec(2), ...
          1 - 2 * qvec(2).^2 - 2 * qvec(3).^2];

end
