code: func (m Mat4) At(row, col int) float64 {
  	return m[col*4+row]
  }
docs: // At returns the matrix element at the given row and column.
  // This is equivalent to mat[col * numRow + row] where numRow is constant
  // (E.G. for a Mat3x2 it's equal to 3)
  //
  // This method is garbage-in garbage-out. For instance, on a Mat4 asking for
  // At(5,0) will work just like At(1,1). Or it may panic if it's out of bounds.