/** Solve A*X = B
        @param  B   A Matrix with as many rows as A and any number of columns.
        @return     X so that L*U*X = B(piv,:)
        @exception  IllegalArgumentException Matrix row dimensions must agree.
        @exception  RuntimeException  Matrix is singular.
        */

        public CoreMatrix solve(CoreMatrix B)
        {
            if (B.getRowDimension() != m)
            {
                throw new Exception("Matrix row dimensions must agree.");
            }
            if (!this.isNonsingular())
            {
                throw new Exception("Matrix is singular.");
            }

            // Copy right hand side with pivoting
            int nx = B.getColumnDimension();
            CoreMatrix Xmat = B.getMatrix(piv, 0, nx - 1);
            double[,] X = Xmat.getArray();

            // Solve L*Y = B(piv,:)
            for (int k = 0; k < n; k++)
            {
                for (int i = k + 1; i < n; i++)
                {
                    for (int j = 0; j < nx; j++)
                    {
                        X[i, j] -= X[k, j] * LU[i, k];
                    }
                }
            }
            // Solve U*X = Y;
            for (int k = n - 1; k >= 0; k--)
            {
                for (int j = 0; j < nx; j++)
                {
                    X[k, j] /= LU[k, k];
                }
                for (int i = 0; i < k; i++)
                {
                    for (int j = 0; j < nx; j++)
                    {
                        X[i, j] -= X[k, j] * LU[i, k];
                    }
                }
            }
            return Xmat;
        }