#------------------------------------------------------------------------------
#  MatrixAdd.py
#------------------------------------------------------------------------------

def matrix_add(A, B):
   """ 
   return a new matrix (i.e. nested list) that is the sum of matrices A and B.
   A and B must be compatible.
   """
   C = []
   for i in range(len(A)):
      R = []
      for j in range(len(A[i])):
         R.append(A[i][j]+B[i][j])
      # end inner for
      C.append(R)
   # end outer for
   return C
# end matrix_add()


#-- main program --------------------------------------------------------------

M = [[1,2,3],[4,5,6],[7,8,9]]
N = [[-1,-2,-3],[-4,-5,-6],[-7,-8,-9]]

P = matrix_add(M, N)
print(P)
print(matrix_add(M,M))

R=[['one','two'],['three','four']]
S=[['five','six'],['seven','eight']]
print(matrix_add(R,S))

print(matrix_add([[1,3],[0,2]],[[2,5],[-3,0]]))