Shortcut to find if a matrix (nxn) is singular or not?

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Discussion Overview

The discussion revolves around finding a quick method to determine if a square matrix (nxn) is singular, exploring various approaches and shortcuts applicable to different matrix sizes, including 2x2, 3x3, and larger matrices.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests that for a 2x2 matrix, the determinant (ad-bc) being zero indicates singularity, questioning if a similar shortcut exists for larger matrices.
  • Another participant notes that while there are various methods to check for singularity, all require some calculation.
  • A participant shares a specific example of a 3x3 matrix and expresses frustration with the lengthy process of determining singularity through Gaussian elimination.
  • One suggestion is to check the eigenvalues of the matrix, stating that if any eigenvalue is zero, the matrix is singular.
  • A later post reiterates the determinant as a method to check singularity but acknowledges the impracticality of calculating it by hand for larger matrices, while also mentioning the availability of computational tools.

Areas of Agreement / Disagreement

Participants do not reach a consensus on a singular shortcut for all nxn matrices, and multiple methods are proposed, indicating a lack of agreement on the most efficient approach.

Contextual Notes

Participants express limitations regarding the practicality of calculating determinants for large matrices and the computational resources available for such tasks.

dlevanchuk
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Is there a quick shortcut to find if a matrix (nxn) is singular or not?

For example, if the matrix is (2x2), and [tex]\Delta[/tex] (i.e. ad-bc) = 0, then matrx is singular and irrevertable..

Is there something similar for (nxn), like (3x3) and (100, 100), without doing the linear independence?
 
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There are different ways to see if a matrix is singular or not, but all of them requires some calculation, as far as I know.
 


then what would be the fastest way to check the singularity of matrix?

lets say my (3x3) matrix is A = [1 2 3; 1 3 2; 1 1 4]. Obviously, if we set Ax = 0, and do G/J elimination we find that this particular matrix is singular... but, man! It takes forever haha.
 


Try to find its eigenvalues - if one of them is 0, then A is singular.
 


dlevanchuk said:
Is there a quick shortcut to find if a matrix (nxn) is singular or not?

For example, if the matrix is (2x2), and [tex]\Delta[/tex] (i.e. ad-bc) = 0, then matrx is singular and irrevertable..

Is there something similar for (nxn), like (3x3) and (100, 100), without doing the linear independence?

Yes, it's called the determinant, but it's not practical to do by hand for big matrices. Luckily there are computers...

http://www.wolframalpha.com/input/?i=det{{1%2C+2%2C+3}%2C+{1%2C+3%2C+2}%2C+{1%2C+1%2C+4}}
 

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