function clone(a) {
    var out = new ARRAY_TYPE(4);
    out[0] = a[0];
    out[1] = a[1];
    out[2] = a[2];
    out[3] = a[3];
    return out;
  }
Creates a new mat2 initialized with values from an existing matrix

@param {mat2} a matrix to clone
@returns {mat2} a new 2x2 matrix