On 31/07/2020 15:59, Mikhael Myara wrote:
Perhaps my example was not clear enough. I start with a fully symbolic
expression. Then, I try two things :
- ask a simplify on the fully symbolic expression, that works well,
- replace some symbols in the initial expression and then simplify.
The first step shows that a simplified expression exists, and
replacing by values may not change this fact (it can lead to an even
more simplified expresssion isn'nt it ?).
I do not understand why Sympy cannot simplify at all the initial
expression when symbols are replaced by values, whereas we know that a
simplified expresssion exists as Sympy itself found it from the fully
symbolic version.
My guess would be that due to rounding errors, when the floating point
numbers get combined - added or subtracted etc. those rounding errors
make what would be exact matches become inexact. For example A-B+B might
be slightly different from A. Put another way, floating point numbers
don't (quite) obey the laws of arithmetic!
I would definitely advise that you work with symbols and integers until
you are ready to substitute floating point numbers.
I can't quite see why you would want to substitute and then simplify.
David
--
You received this message because you are subscribed to the Google Groups
"sympy" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
To view this discussion on the web visit
https://groups.google.com/d/msgid/sympy/4747234e-c1a7-8eb9-c3fb-5f929facca49%40dbailey.co.uk.
