def _solve( self, b ):
        x = Vec([])
        for i in range(self.rows-1, -1, -1):
            assert NPRE or self[i][i], 'Backsub requires non-zero elements on the diagonal'
            x.insert(0, (b[i] - x.dot(self[i][i+1:])) / self[i][i] )
        return x
Solve an upper triangular matrix using backward substitution
dataset/ETHPy150Open sunlightlabs/clearspending/completeness/statlib/matfunc.py/UpperTri._solve