Artifact ad8998bb99a43250f9616ab0fe8f03d46da8e46b
//-------------------------------------------------------------
// Linear Equation Solver
// O(n^3)
//
// Verified by
// - SRM 398 Div1 LV3
// - AOJ 0004
//-------------------------------------------------------------
vector<double> solve_linear_eq( int n, vector< vector<double> > M, const vector<double>& V )
{
vector<double> A(V);
for(int i=0; i<n; ++i)
{
// pivot
if( M[i][i] == 0 )
for(int j=i+1; j<n; ++j)
if( M[j][i] != 0 )
{swap(M[i], M[j]); swap(A[i], A[j]); break;}
if( M[i][i] == 0 )
throw "no anser";
// M[i][i] <-- 1
double p = M[i][i];
for(int j=i; j<n; ++j)
M[i][j] /= p;
A[i] /= p;
// M[*][i] <-- 0
for(int j=0; j<n; ++j) if(j!=i)
{
double r = M[j][i];
for(int k=i; k<n; ++k)
M[j][k] -= M[i][k] * r;
A[j] -= A[i] * r;
}
}
return A;
}