Code for determinant.
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eden hazard
il 14 Nov 2018
Commentato: Walter Roberson
il 26 Feb 2021
I would like to built a code to find the determinant of a 24x24 matrix.I dont want to use the det(X) function,but a fuction that would be quick.
The one i created,whick is too slow for that.
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/195073/image.jpeg)
2 Commenti
Stephen23
il 15 Nov 2018
"I dont want to use the det(X) function,but a function that would be quick."
Ah, the sweet, blind optimism of youth.
Have you actually looked at the definition of the determinant, and figured out how many calculations it would require for a 24x24 matrix? When is your estimated completion?
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John D'Errico
il 15 Nov 2018
NO NO NO!!!!!
First, you should not be using the determinant here. I don't know why you think you need to use it. But if you don't understand how to efficiently compute a determinant, the probability is 1 that you should not be using the determinant in the first place. There are far better tools to determine is amatrix issingular, which is why you are surely wanting to compute the determinant of a 24x24 matrix.
Ok, why is the code you wrote a an obscenely bad one? Do you understand that the code you wrote will require O(factorial(24)) computations to execute?
factorial(24)
ans =
6.20448401733239e+23
Even the largest supercomputer the NSA owns would grind to a miserable halt.
So, CAN you compute the determinant more efficiently? Well, yes. USE DET! (In fact there are ways to compute the determinant efficiently. But since you should not be using it in the first place, I won't go into details.)
So better yet, don't compute the determianant at all. So instead, you need to learn how to use tools like rank, cond or svd to do what you are trying to do. Of course, we don't really yet know what you are doing.
6 Commenti
James Tursa
il 15 Nov 2018
Modificato: James Tursa
il 15 Nov 2018
My teacher in college once described the minors/cofactor method to me this way:
"Well, it may be slow, but it's innacurate!"
Steven Lord
il 16 Nov 2018
"innaccurate" as in "start it computing, go to bed, and maybe you'll have something close to right when you wake up?" grin
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Reza Lashani
il 3 Feb 2021
Modificato: Reza Lashani
il 3 Feb 2021
One of the fastest ways to determine the determinant of a matrix is doing row operation. For an invertible matrix we know that row operations finally reach to identity matrix which has determinant equal to 1. For calculating determinant we can write an efficient and of course fast code to do row operation and it is not necessary to make the first non-zero entry 1 by dividing it by itself. It cause we finally reach to a diagonal matrix (stead of identity matrix) and the determinant is equal to the product of pivots of the final matrix. Doing this algorithm on my ordinary system for a 24 × 24 matrix lates less than 1 second.
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