On Wed, 10 Feb 2021 at 20:24, Aaron Meurer <asmeu...@gmail.com> wrote: > > On Wed, Feb 10, 2021 at 6:47 AM David Bailey <d...@dbailey.co.uk> wrote: >> >> On 10/02/2021 00:53, Oscar Benjamin wrote: >> >> On Tue, 9 Feb 2021 at 23:58, S.Y. Lee <sylee...@gmail.com> wrote: >> >> >> And we would also arrive in questions like: If equation brings its own >> algebra system, there should be an equation of equations? How should we >> solve them? >> >> It's not an "algebra system": it's just a few convenience operations. >> It should not be confused with allowing Equation to be used in places >> where Expr is expected. >> >> Might it be an idea to introduce functions such as AddSides, SubtractSides, >> etc that Mathematica has? Not only would these avoid any confusion with the >> normal arithmetic operations, but I think using these functions would >> clarify what is going on. After all, when people do such operations by hand, >> they don't write (a=b)*k,or whatever, they typically write "Multiplying >> equation 4 by k we get..." > > > Is there a need to have an unevaluated version of AddSides? + already works > for an evaluated version. > > It might be worth thinking about inequalities in the design here. We've been > ignoring them because it's simpler to do equalities first, but inequalities > have some restrictions that might clarify what design we want. For a > b, > things like function application or even multiplication aren't > straightforward. What should x*(a > b) do if x is only known to be real? One > option is a Piecewise, but then things get hairy if you start doing other > operations. Maybe a MultiplySides does actually make sense for this.
See also these two links: https://github.com/sympy/sympy/pull/20723#issuecomment-763975854 https://github.com/sympy/sympy/pull/17097 Yes, DivideSides would make sense for unevaluated division of inequalities etc. That is not inconsistent with using + though: We can use eq1+eq2 as a shorthand for the evaluated form of AddSides(eq1, eq2). For equations that would always be able to evaluate. In Mathematica this is all organised around making Boolean expressions that can evaluate after substitution. Oscar -- 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 sympy+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/sympy/CAHVvXxTAAA%3DHDaNA4-HU%2BqFV34nF7GfA7GbHn_HzVWgu0Epr6w%40mail.gmail.com.
