function multiplyScalarAndAdd(out, a, b, scale) {
  out[0] = a[0] + b[0] * scale;
  out[1] = a[1] + b[1] * scale;
  out[2] = a[2] + b[2] * scale;
  out[3] = a[3] + b[3] * scale;
  out[4] = a[4] + b[4] * scale;
  out[5] = a[5] + b[5] * scale;
  return out;
}
Adds two mat2d's after multiplying each element of the second operand by a scalar value.

@param {mat2d} out the receiving vector
@param {mat2d} a the first operand
@param {mat2d} b the second operand
@param {Number} scale the amount to scale b's elements by before adding
@returns {mat2d} out