# File lib/matrix.rb, line 494
  def +(m)
    case m
    when Numeric
      Matrix.Raise ErrOperationNotDefined, "+"
    when Vector
      m = Matrix.column_vector(m)
    when Matrix
    else
      x, y = m.coerce(self)
      return x + y
    end
    
    Matrix.Raise ErrDimensionMismatch unless row_size == m.row_size and column_size == m.column_size
    
    rows = (0 .. row_size - 1).collect {
      |i|
      (0 .. column_size - 1).collect {
        |j|
        self[i, j] + m[i, j]
      }
    }
    Matrix.rows(rows, false)
  end