Calculate the determinant of any matrix about ublas

[abhishekkranjan]

Hi @abhishekkranjan, this is not the place to post such question :-). Try a forum instead 👍

am really sorry for posting that question, I was unaware of it.

[abhishekkranjan]

Hi @abhishekkranjan, this is not the place to post such question :-). Try a forum instead +1

yes. we can discuss it either directly in gitter: https://gitter.im/boostorg/ublas
or use the mailing list: [email protected]

thanks, i have joined the gitter room

[penguian]

Hi Richel,
How does your algorithm compare in speed and stability vs (e.g.) Householder QR decomposition? https://en.m.wikipedia.org/wiki/QR_decomposition#Connection_to_a_determinant_or_a_product_of_eigenvalues
All the best, Paul

On 18 April 2016 7:41:16 PM AEST, Richel Bilderbeek [email protected] wrote:

Boost.uBLAS can calculate the determinant of (at most) 2x2 matrices. I
have a piece of code that can do this for any matrix size (which is
http://www.richelbilderbeek.nl/CppUblasMatrixExample7.htm), that
already has been tested.

If accepted, I volunteer to try to add this to Boost, but I'd need some
help to up the quality even more.

Is this already been done? If no, would it be appreciated if I (create
and) submit a Pull Request?

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#38

Paul Leopardi - http://sites.google.com/site/paulleopardi/

[richelbilderbeek]

Undo: AFAIK I do not use Householder QR decomposition. I cannot remember the algorithm name I used. I do remember it was something using 2x2 matrices as a building block for bigger ones.

[GuillermoCasas]

I have been using this algorithm in my research and has given me no problems for inverting 10x10 matrices coming from a spacial least-squares polynomial fitting problem. It seems reasonably fast, although I've only used it in small systems (about 25 times per node, for about 2500 nodes).
Well done, Richel.

[abhishekkranjan]

Am not getting pr, can you please help how can i contribute my code to calculate the determinant of any matrix.
//My cpp code
// C++ program to find Deteminant of a matrix
#include <bits/stdc++.h>
using namespace std;

// Dimension of input square matrix
#define N 4
// Function to get determinant of matrix
int determinantOfMatrix(int mat[N][N], int n)
{
int num1, num2, det = 1, index,
total = 1; // Initialize result

// temporary array for storing row
int temp[n + 1];

// loop for traversing the diagonal elements
for (int i = 0; i < n; i++) 
{
	index = i; // initialize the index

	// finding the index which has non zero value
	while (mat[index][i] == 0 && index < n) 
	{
		index++;
	}
	if (index == n) // if there is non zero element
	{
		// the determinat of matrix as zero
		continue;
	}
	if (index != i) 
	{
		// loop for swaping the diagonal element row and
		// index row
		for (int j = 0; j < n; j++) 
		{
			swap(mat[index][j], mat[i][j]);
		}
		// determinant sign changes when we shift rows
		// go through determinant properties
		det = det * pow(-1, index - i);
	}

	// storing the values of diagonal row elements
	for (int j = 0; j < n; j++) 
	{
		temp[j] = mat[i][j];
	}
	// traversing every row below the diagonal element
	for (int j = i + 1; j < n; j++) 
	{
		num1 = temp[i]; // value of diagonal element
		num2 = mat[j][i]; // value of next row element

		// traversing every column of row
		// and multiplying to every row
		for (int k = 0; k < n; k++) 
		{
			// multiplying to make the diagonal
			// element and next row element equal
			mat[j][k]
				= (num1 * mat[j][k]) - (num2 * temp[k]);
		}
		total = total * num1; // Det(kA)=kDet(A);
	}
}

// mulitplying the diagonal elements to get determinant
for (int i = 0; i < n; i++) 
{
	det = det * mat[i][i];
}
return (det / total); // Det(kA)/k=Det(A);

}

// Driver code
int main()
{
/*int mat[N][N] = {{6, 1, 1},
{4, -2, 5},
{2, 8, 7}}; */

int mat[N][N] = { { 1, 0, 2, -1 },
				{ 3, 0, 0, 5 },
				{ 2, 1, 4, -3 },
				{ 1, 0, 5, 0 } };

// Function call
printf("Determinant of the matrix is : %d",
	determinantOfMatrix(mat, N));
return 0;

}

[richelbilderbeek]

Hi @abhishekkranjan, this is not the place to post such question :-). Try a forum instead 👍

[bassoy]

Hi @abhishekkranjan, this is not the place to post such question :-). Try a forum instead +1

yes. we can discuss it either directly in gitter: https://gitter.im/boostorg/ublas
or use the mailing list: [email protected]