View Compilation Error

0_0_4361230_28608.cpp: In member function `Matrix Matrix::pow(int)':
0_0_4361230_28608.cpp:48: error: `O' undeclared (first use this function)
0_0_4361230_28608.cpp:48: error: (Each undeclared identifier is reported only once for each function it appears in.)
0_0_4361230_28608.cpp: At global scope:
0_0_4361230_28608.cpp:54: error: `Matrix O' used prior to declaration