function add(out, a, b) {
  out[0] = a[0] + b[0];
  out[1] = a[1] + b[1];
  out[2] = a[2] + b[2];
  out[3] = a[3] + b[3];
  out[4] = a[4] + b[4];
  out[5] = a[5] + b[5];
  out[6] = a[6] + b[6];
  out[7] = a[7] + b[7];
  out[8] = a[8] + b[8];
  out[9] = a[9] + b[9];
  out[10] = a[10] + b[10];
  out[11] = a[11] + b[11];
  out[12] = a[12] + b[12];
  out[13] = a[13] + b[13];
  out[14] = a[14] + b[14];
  out[15] = a[15] + b[15];
  return out;
}
Adds two mat4's

@param {mat4} out the receiving matrix
@param {mat4} a the first operand
@param {mat4} b the second operand
@returns {mat4} out