MATLAB Answers

Does symbolics give wrong results?

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Kiran Sagar
Kiran Sagar on 10 Dec 2015
Answered: Walter Roberson on 11 Dec 2015
I was doing matrix operations using symbolics, I found out to my surprise, that the results where wrong and unrepeatable. Same operations gave different results. For example, I calculated the expression K- K.' to check if the matrix was symmetric. I use this expression on command line twice and I get different results each time.


Jan on 10 Dec 2015
Please post the code, which reproduces the problem. Otherwise it is impoosible to guess, what's going on on your computer.
Stephen Cobeldick
Stephen Cobeldick on 10 Dec 2015
Well, it is easy to guess, but the chance of guessing correctly is very slim. My guess is aliens.

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Answers (1)

Walter Roberson
Walter Roberson on 11 Dec 2015
Symbolic routines are not required to give identical output each time they are called, even if nothing is redefined and no new assume() are added and so on. However, it is expected that the results will be mathematically equivalent (except possibly at some singularities.)
You should try using simplify() on the two different versions


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