There is a lot of discussion about this in these issues
https://github.com/sympy/sympy/issues/5031
https://github.com/sympy/sympy/issues/4986
https://github.com/sympy/sympy/issues/14741
Aaron Meurer
On Thu, May 2, 2019 at 7:34 AM <schweg...@gmail.com> wrote:
>
> Hello Sympy Developers and Interested People!
>
> First off, Thank you very much for your great effort and success - Sympy is
> an absolutely awesome piece of software!
> I am using it for the better of 2 years now and did some fun stuff, but I
> still haven't really decided on a coherent way of writing equations. The
> problem is that Eq() is not an equation in the mathematical sense as the
> following examples should demonstrate:
>
> t = S('t')
> f = Function('f')(t)
> g = Function('g')(t)
>
> equation = Eq(f,g+1)
> equation2 = equation-1
> equation3 = equation.diff(t)
> equation4 = equation.subs(equation) # this I can do with subs(*equation.args)
>
> Having a symbolic comparison of terms seems useful to me, so I totally get
> equation and Eq and their meaning.
> However, an equation class satsifying the mathematics for the above examples
> seems to be absent in sympy.
>
> What I am proposing is to think of a way that equations are made a basic
> building block in mathematics and imho should be likewise in a mathematics
> tool.
> That said, I know ways to do all of the above, but it is really not intuitive
> to have every expression in a "x-y=0" form.
> I would think that next to nobody actually thinks like that. And the code is
> hard to subsitute, because you need to do
>
> eq = g+1-f
> eq.subs(f,eq+f)
>
> or even worse looking use solve.
>
> Another big thing is printing. Printing "x-y" is very hard to read and you
> need to explain this unconfort to any new user.
> Having "x=y" would be just as everyone learns in maths.
>
> Programmatically I don't think that a new equation class, or the changes to
> Eq() would be a huge deal.
> But programming it myself and then using a non-standard for something as
> standard as an equation seems really bad practice.
> What do you guys think about that?
>
> Thanks again
> Mike
>
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