ok I forgot variables declaration ...
Le vendredi 31 juillet 2020 23:06:01 UTC+2, Oscar a écrit :
>
> On Fri, 31 Jul 2020 at 21:06, Mikhael Myara
> <mikhae...@umontpellier.fr <javascript:>> wrote:
> >
> > Le vendredi 31 juillet 2020 20:46:08 UTC+2, Oscar a écrit :
> >>
> >> On Fri, 31 Jul 2020 at 17:26, Mikhael Myara
> >> <mikhae...@umontpellier.fr> wrote:
> >> >
> >> > Thanks for your answer.
> >> >
> >> > I don’t do it « for sport » ;-) My example is a reduced example
> coming from a practical situation I encountered.
> >>
> >> I understand that you have reduced this but it is a lot better if the
> >> reduction is self-contained so that others can literally copy-paste
> >> the code to test what is happening with an expression that
> >> demonstrates the issue. I could probably tell you exactly what the
> >> problem is in a given example if you provided minimal code for that
> >> example.
> >>
> > That's what I did in my first post + screen copies :
> >>
> >> import sympy as sp
> >>
> >> H=-(-CB*Ve*s*(-CA*s - 1/RA)**2/(RB*(CB*s + 1/RB)*(CA*s - (-CA*s -
> 1/RA)**2/(CA*s - CB**2*s**2/(CB*s + 1/RB) + CB*s + 1/RA) + 2/RA)*(CA*s -
> CB**2*s**2/(CB*s + 1/RB) + CB*s + 1/RA)) - CB*Ve*s/(RB*(CB*s +
> 1/RB)))/(Ve*(CA*s - CB**2*s**2/(CB*s + 1/RB) + CB*s + 1/RA))
>
> Have you tried copy-pasting that? I get this:
>
> Traceback (most recent call last):
> File "<stdin>", line 1, in <module>
> NameError: name 'CB' is not defined
>
> Of course I'm being pedantic because I can guess that all of those are
> supposed to be symbols but it takes some time for me to figure out
> what symbols they are and write the small piece of code that defines
> them (presumably that's what Aaron did). More importantly there are
> multiple ways to define a symbol (real, positive, ...) and some
> simplifications depend on that so even if I do fill in the missing
> code then I won't know if I'm seeing the same behaviour as you.
>
> >> > I developed a small software that solves the voltages and currents of
> an electronic circuit described by means of a standard format (« netlist
> »). This file is parsed, equations are solved. In this netlist file, the
> values of the components are given.
> >>
> >> How exactly are they given in the file (e.g. to how many digits)?
> >>
> >> If the file has something like 0.12 then you can read that in directly
> >> as Rational('0.12') rather than converting the string to a float. Then
> >> you will have an object that represents the value from the file
> >> exactly with no rounding error. Alternatively you can use nsimplify to
> >> convert the floats to an approximate rational representation (direct
> >> string to Rational is better though).
> >
> > Values can change a lot, from 1é-10 to 1e10 typically. In most cases 2
> to 3 significant numbers, but can be much more.
>
> It sounds like these would be fine to parse directly as Rational when
> reading the file:
>
> >>> from sympy import *
> >>> Rational('1e-10')
> 1/10000000000
> >>> Rational('0.112345e-10')
> 22469/2000000000000000
>
> If you want to display the result with decimal dot notation then you
> can convert the Rationals in any expression to Float at the end for
> printing using the nfloat function:
>
> >>> nfloat(_)
> 1.12345000000000e-11
>
>
> --
> Oscar
>
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