# Untitled

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```import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Random;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;

public class Main {

static List<double[][]> generateMatrix(int nuknowns) {
var random = new Random();

var coefs = new double[nuknowns][nuknowns];
var xs = new double[nuknowns];
for (int i = 0; i < nuknowns; i++)
xs[i] = random.nextDouble(-10, 10);
var b = new double[1][nuknowns];
for (int i = 0; i < nuknowns; i++) {
double curB = 0.;
for (int j = 0; j < nuknowns; j++) {
var c = random.nextDouble(-10, 10);
coefs[i][j] = c;
curB += xs[j] * c;
}
b[0][i] = curB;
}
return List.of(coefs, b);
}

static void elimRow(double[] A, double[] K, double[] B, int i, int k) {
double factor = A[k] / K[k];
B[i] -= factor * B[k];
for (int j = k; j < A.length; j++)
A[j] -= factor * K[j];
}

public static void solveInParallel(double[][] A, double[] B) throws ExecutionException, InterruptedException {
int N = B.length;
for (int k = 0; k < N; k++) {
/** find pivot row **/
int max = k;
for (int i = k + 1; i < N; i++)
if (Math.abs(A[i][k]) > Math.abs(A[max][k]))
max = i;
/** swap row in A matrix **/
double[] temp = A[k];
A[k] = A[max];
A[max] = temp;
/** swap corresponding values in constants matrix **/
double t = B[k];
B[k] = B[max];
B[max] = t;

/** pivot within A and B **/
Future[] futures = new Future[N-k-1];
for (int i = k + 1; i < N; i++) {

int finalI1 = i;
int finalK1 = k;
futures[i-k-1] = executor.submit(() -> elimRow(A[finalI1], A[finalK1], B, finalI1, finalK1));
}
for (Future f : futures) f.get();
}
/** back substitution **/
double[] solution = new double[N];
for (int i = N - 1; i >= 0; i--) {
double sum = 0.0;
for (int j = i + 1; j < N; j++)
sum += A[i][j] * solution[j];
solution[i] = (B[i] - sum) / A[i][i];
}
}

//do the same thing but with parallel matricies

//what can you do here
public static void main(String[] args) throws ExecutionException, InterruptedException {

for (int i = 1000; i <= 3000; i += 50) {
List<double[][]> doubles = generateMatrix(i);

long s1 = System.currentTimeMillis();
solveInParallel(doubles.get(0), doubles.get(1)[0]);
long t2 = System.currentTimeMillis() - s1;

System.out.println(t2);
}

executor.shutdown();
}
}
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```