function copy(out, a) {
    out[0] = a[0];
    out[1] = a[1];
    out[2] = a[2];
    out[3] = a[3];
    return out;
  }
Copy the values from one mat2 to another

@param {mat2} out the receiving matrix
@param {mat2} a the source matrix
@returns {mat2} out