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Why Does My Solve Linear Equations VI Give an Unexpected Solution Vector?

Primary Software:
Primary Software Version: 2013
Primary Software Fixed Version: N/A
Secondary Software: N/A

I want to solve the equation AX = B for X, where A is the known matrix, X is the unknown vector, and B is the known vector. However, when using the Solve Linear Equations VI, the resultant B does not appear to be correct. When multiplying AX to check my result, I get a vector that is not B. Why does this occur?

This can occur when the input matrix, A, for the Solve Linear Equations VI is singular. When this is the case, instead of solving the equation AX = B for X, LabVIEW finds the least-square solution which is the solution with the least square mean error. This is because there is no solution for AX = B.

To check if a matrix is singular, you must determine whether the determinant is zero. If the determinant is zero, the matrix is singular. The easiest way to check this would be to use a Determinant VI to obtain the determinant.

Shown below is a VI snippet that demonstrates how a singular matrix can give a misleading solution. The snippet also demonstrates how to use the Determinant VI to test and see if a matrix is singular.

Related Links:
LabVIEW Help: Solve Linear Equations VI
External Link: Invertible matrix - Wikipedia, the free encyclopedia

Singular Matrix

Report Date: 09/24/2002
Last Updated: 09/13/2013
Document ID: 2PNGS2A2

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