On 11/02/2021 20:44, Aaron Meurer wrote:
How would you handle dividing both sides of an equation by something?
I don't know if a piecewise makes sense. (a = b)/x would be "a/x = b/x
if x != 0, ??? otherwise". What meaningful thing could the ??? be? You
can easily manipulate an equation into nonsense if you aren't careful
about this (just Google "proof that 1 = 2"). But I don't know if SymPy
should try to take responsibility to prevent it.
This is exactly why I think it would be good to give the users
DivideSides, and MultiplySides, which they could use as they saw
appropriate, rather than eqn(a,b)/c, etc. SymPy would not take
responsibility for this mathematical operation. To me, this is exactly
analogous to subs:
cos(x).subs(cos,sin)
sin(x)
SymPy does not guarantee that this is valid!
Also there is absolutely no sense in which eqn(a,b) is twice as big as
eqn(a,b)/2, so is it desirable that the notation should suggest that it is?
David
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