How to Solve Equations with a Singular Matrix?

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    Determinant Matrices
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Discussion Overview

The discussion revolves around methods for solving systems of equations represented by singular matrices, specifically when the determinant is zero. Participants explore various approaches and considerations related to the implications of singularity in the context of two equations with two unknowns.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant asks how to solve a singular matrix, providing an example of a system of two equations and noting the determinant condition.
  • Another participant explains that a singular matrix may lead to either no solutions or an infinite number of solutions, providing two examples to illustrate these cases.
  • Some participants suggest methods such as LU decomposition and Gaussian elimination but express uncertainty about their applicability when the determinant is zero.
  • One participant mentions focusing on systems with a nonzero discriminant to find unique solutions and suggests using Cramer's Rule in such cases.
  • Another participant proposes looking up algorithms for computing the "generalized inverse" of a matrix as a potential method for dealing with singular matrices.

Areas of Agreement / Disagreement

Participants express differing views on the applicability of various methods for solving singular matrices, with no consensus on a single approach. Some agree on the implications of singularity while others propose different strategies.

Contextual Notes

Participants note that the system of equations may have either no solutions or an infinite number of solutions when the determinant is zero, but do not resolve the implications of these conditions fully.

nelectrode
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Hi,

How would you solve a singular matrix? ie when determinant is zero.

Lets assume an equation, (1) Ax+By=E and (2) Cx+Dy=F

if the determinant; AD-BC = 0, and therefore the matrix is singular, How to go around solving the equation?

LU decomposition, Gaussian elimination?

Ideally I am looking for a method which could be "easily" implemented in a code.

Thanks
 
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nelectrode said:
Hi,

How would you solve a singular matrix? ie when determinant is zero.

Lets assume an equation, (1) Ax+By=E and (2) Cx+Dy=F
That is a system of two equations (not one) in two unknowns, so presumably your matrix is 2 x 2.
nelectrode said:
if the determinant; AD-BC = 0, and therefore the matrix is singular, How to go around solving the equation?
The system might have no solution or it might have an infinite number of solutions.
A couple of examples might help to shed some light here.
Example 1.
x + 2y = 3
2x + 4y = 6
The equations in this system are equivalent, so geometrically the two equations represent a single line. Here there are an infinite number of solutions. Each point on the first line is also on the second line.

Example 2.
x + 2y = 3
2x + 4y = 1
The equations in this system represent two parallel lines with no common point of intersection. The system has no solutions.

nelectrode said:
LU decomposition, Gaussian elimination?

Ideally I am looking for a method which could be "easily" implemented in a code.
Assuming that your systems consist of two equations in two unknowns, I would focus my efforts on those systems for which the discriminant is nonzero (i.e., the systems that have a unique solution). Once you determine that the discriminant is nonzero, you could use Cramer's Rule to determine the solution.

If the discriminant is zero, I don't see any point in trying to use Gaussian elimination or LU decomposition. In a system of two equations with two unknowns for which the discrimant is zero, there will either be an infinite number of solutions or no solution at all.
 
thanks a lot :smile:
 
nelectrode said:
How to go around solving the equation?

LU decomposition, Gaussian elimination?

Ideally I am looking for a method which could be "easily" implemented in a code.

Look up algorithms for computing the "generalized inverse" of a matrix.
 

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