How to find det of matrix 3x3 in c#

Question

I'm able to find det of matrix 2x2 using this code:

using System;

class find_det
{
static void Main()
{
    int[,] x = { { 3, 5, }, { 5, 6 }, { 7, 8 } };
    int det_of_x = x[0, 0] * x[1, 0] * x[0, 1] * x[1, 1];
    Console.WriteLine(det_of_x);
    Console.ReadLine();
}
}

But when I tried to find det of 3x3 Matrix, using this code:

using System;

class matrix3x3
{
    static void Main()
{
    int[,,] x={{3,4,5},{3,5,6},{5,4,3}};
    int det_of_x=x[0,0]*x[0,1]*x[0,2]*x[1,0]*x[1,1]*x[1,2]*x[2,0]*x[2,1]*x[2,2];
    Console.WriteLine(det_of_x);
    Console.ReadLine();
    }
}

It got error. Why?

Horribly vague question. The error from your compiler should've given you atleast a hint of what is wrong here. But as the other's have said, it's still a 2D Array, not a 3D, remove the extra , in the type. — Eric Johansson, Feb 16 '13 at 13:27
see http://stackoverflow.com/questions/5051528/how-to-calculate-matrix-determinant-nn-or-just-55 — Rachel Gallen, Feb 16 '13 at 13:28
I don't know what you are calculating but it's also not the determinant of a matrix. The determinant of a 2x2 matrix A is det(A) = a11*a22 - a12*a21. — Dirk, Feb 16 '13 at 13:44

Guffa · Answer 1 · 2013-02-16T13:31:49.447

2

It's still a two dimensional array (int[,]) not a three dimensional array(int[,,]).

int[,] x = { { 3, 4, 5 }, { 3, 5, 6 }, { 5, 4, 3 } };

Side note: You can do that calculation for any multidimensional array like this:

int det_of_x = 1;
foreach (int n in x) det_of_x *= n;

edited Feb 16 '13 at 13:31

answered Feb 16 '13 at 13:25

Guffa

687,336
108
737
1,005

Damnn, I thought that 2d matrix are 2x2 while 3d are 3x3. Thank you for your time. I got the problem solve. – user2078395 Feb 16 '13 at 14:11

score 2 · Answer 2 · answered Feb 16 '13 at 13:25

2

You've declared a 3D array in the second example, not a 3x3 2D array. Remove the extra "," from the declaration.

answered Feb 16 '13 at 13:25

Matthew Watson

104,400
10
158
276

score 1 · Answer 3 · answered Feb 16 '13 at 13:25

1

Because you have a 3 dimensional array and are using it like a 2 dimensional one such as x[0,0].

answered Feb 16 '13 at 13:25

Yuriy Faktorovich

67,283
14
105
142

Soner Gönül · Answer 4 · 2013-02-16T13:44:15.043

What you declared it a still two dimensional array. For 2D array you can use it like this;

int[,] x = { { 3, 4, 5 }, { 3, 5, 6 }, { 5, 4, 3 } };
int det_of_x = x[0, 0] * x[0, 1] * x[0, 2] * x[1, 0] * x[1, 1] * x[1, 2] * x[2, 0] * x[2, 1] * x[2, 2];
Console.WriteLine(det_of_x);
Console.ReadLine();

If you want to use 3 dimensional array, you should use it like int[, ,]

Check out more informations about Multidimensional Arrays from MSDN.

Since arrays implements IEnumerable and IEnumerable<T>, you can use foreach iteration on all arrays in C#. In your case, you can use it like this;

int[, ,] x = new int[,,]{ {{ 3, 4, 5 }, { 3, 5, 6 }, { 5, 4, 3 }} };
int det_of_x = 1;
foreach (var i in x)
{
    det_of_x *= i;
}

Console.WriteLine(det_of_x); // Output will be 324000

Here is a DEMO.

How to find det of matrix 3x3 in c#

4 Answers4