function copy(out, a) {
  out[0] = a[0];
  out[1] = a[1];
  out[2] = a[2];
  out[3] = a[3];
  out[4] = a[4];
  out[5] = a[5];
  out[6] = a[6];
  out[7] = a[7];
  out[8] = a[8];
  return out;
}
Copy the values from one mat3 to another

@param {mat3} out the receiving matrix
@param {mat3} a the source matrix
@returns {mat3} out