View Compilation Error

0_0_29249025_11198.cpp: In function 'int main()':
0_0_29249025_11198.cpp:82:65: error: 'sgn' was not declared in this scope
                 while(ld<cursize && ld<le && sgn(v[j].dot(v[ld]))>0)ld++;
                                                                 ^