Technical Solutions

Why is the result of multiplying a matrix by its inverse different from the identity matrix returned by the EYE function in MATLAB?

Date Last Modified: Friday, June 26, 2009

Solution ID:		1-536MBF
Product:		MATLAB
Reported in Release:		No Release
Platform:		All Platforms
Operating System:		All OS

 

Subject:

Why is the result of multiplying a matrix by its inverse different from the identity matrix returned by the EYE function in MATLAB?

Problem Description:

I created a matrix and computed its inverse using the INV command. However, when I multiply them together, and compare the result to the identity matrix using the ISEQUAL function, the result is 'false' or 0. For example:
a = rand(5);
b = inv(a);
isequal(a*b,eye(5))


ans =

     0

Solution: This behavior is related to floating-point arithmetic and the way numbers are represented in a computer. For more information on this subject, see the related Solution below.

 

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