View Compilation Error

0_0_2965735_26909.cpp: In function `mat plus(mat&, int)':
0_0_2965735_26909.cpp:53: error: `plus' undeclared (first use this function)
0_0_2965735_26909.cpp:53: error: (Each undeclared identifier is reported only once for each function it appears in.)
0_0_2965735_26909.cpp: In function `int main()':
0_0_2965735_26909.cpp:93: error: `plus' undeclared (first use this function)