Has the inv() function changed?

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Won-Ho Song 2017-9-19

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https://ww2.mathworks.cn/matlabcentral/answers/357310-has-the-inv-function-changed

编辑： Won-Ho Song 2017-9-19

A2011.mat

I am wondering whether the inverse matrix function, inv(), has changed. I have two versions of MATLAB, 2011b (win64, 7.13.0.564) and 2016a (win64, 9.0.0.341360). I found out that, for some matrix, the results of inverse matrix are different in the two versions of MATLAB. Consider the attached matrix I generated.

Download the A2011.mat file and load in the MATLAB. Calculate B=inv(A'*A). Then, the results of inverse matrix are different! Thus, I am wondering whether the inverse matrix function has changed between 2011b and 2016a. Thank you.

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Stephen23 2017-9-19

@Won-Ho Song: please edit your question and upload the .mat file here by clicking the paperclip button. It is not appreciated having links to random third-party websites.

Rik 2017-9-19

The release notes are not always comprehensive, but it is the first place to look: your search term.

Sidenote: I seem to recall a function like inv is very tricky to implement in a way that is both fast and numerically stable. For some functions it is indeed the case that a re-worked implementation sacrifices some numerical stability for a large increase in speed (or supported dimensions). I don't know if this is the case for inv. At any rate, your results should always be reversible within machine precision.

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