code: import static java.util.Arrays.stream;
  import java.util.Locale;
  import static java.util.stream.IntStream.range;
  
  public class Test {
  
      static double dotProduct(double[] a, double[] b) {
          return range(0, a.length).mapToDouble(i -> a[i] * b[i]).sum();
      }
  
      static double[][] matrixMul(double[][] A, double[][] B) {
          double[][] result = new double[A.length][B[0].length];
          double[] aux = new double[B.length];
  
          for (int j = 0; j < B[0].length; j++) {
  
              for (int k = 0; k < B.length; k++)
                  aux[k] = B[k][j];
  
              for (int i = 0; i < A.length; i++)
                  result[i][j] = dotProduct(A[i], aux);
          }
          return result;
      }
  
      static double[][] pivotize(double[][] m) {
          int n = m.length;
          double[][] id = range(0, n).mapToObj(j -> range(0, n)
                  .mapToDouble(i -> i == j ? 1 : 0).toArray())
                  .toArray(double[][]::new);
  
          for (int i = 0; i < n; i++) {
              double maxm = m[i][i];
              int row = i;
              for (int j = i; j < n; j++)
                  if (m[j][i] > maxm) {
                      maxm = m[j][i];
                      row = j;
                  }
  
              if (i != row) {
                  double[] tmp = id[i];
                  id[i] = id[row];
                  id[row] = tmp;
              }
          }
          return id;
      }
  
      static double[][][] lu(double[][] A) {
          int n = A.length;
          double[][] L = new double[n][n];
          double[][] U = new double[n][n];
          double[][] P = pivotize(A);
          double[][] A2 = matrixMul(P, A);
  
          for (int j = 0; j < n; j++) {
              L[j][j] = 1;
              for (int i = 0; i < j + 1; i++) {
                  double s1 = 0;
                  for (int k = 0; k < i; k++)
                      s1 += U[k][j] * L[i][k];
                  U[i][j] = A2[i][j] - s1;
              }
              for (int i = j; i < n; i++) {
                  double s2 = 0;
                  for (int k = 0; k < j; k++)
                      s2 += U[k][j] * L[i][k];
                  L[i][j] = (A2[i][j] - s2) / U[j][j];
              }
          }
          return new double[][][]{L, U, P};
      }
  
      static void print(double[][] m) {
          stream(m).forEach(a -> {
              stream(a).forEach(n -> System.out.printf(Locale.US, "%5.1f ", n));
              System.out.println();
          });
          System.out.println();
      }
  
      public static void main(String[] args) {
          double[][] a = {{1.0, 3, 5}, {2.0, 4, 7}, {1.0, 1, 0}};
  
          double[][] b = {{11.0, 9, 24, 2}, {1.0, 5, 2, 6}, {3.0, 17, 18, 1},
          {2.0, 5, 7, 1}};
  
          for (double[][] m : lu(a))
              print(m);
  
          System.out.println();
  
          for (double[][] m : lu(b))
              print(m);
      }
  }
  