int array2d[3][2];

void setup() {
  // put your setup code here, to run once:
  randomSeed(analogRead(0));
  Serial.begin(9600);

  for(int i = 0; i < 3; i++){
    for(int j = 0; j < 2; j++){
      array2d[i][j] = random(-5, 0);
    }
  }

  Serial.println("Matrix:");
  for(int i = 0; i < 3; i++){
    for(int j = 0; j < 2; j++){
      Serial.print(array2d[i][j]);
      Serial.print("\t");
    }
    Serial.println();
  }
}

void loop() {
  // put your main code here, to run repeatedly:

}