View Compilation Error

0_0_6500204_5075.cpp: In function `matrix cal(matrix, int, int, int)':
0_0_6500204_5075.cpp:155: error: invalid initialization of non-const reference of type 'matrix&' from a temporary of type 'matrix'
0_0_6500204_5075.cpp:138: error: in passing argument 2 of `matrix mul_mod(matrix&, matrix&, int, int)'