#18396: Handle substitutions of partial sums and products
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Reporter: vdelecroix | Owner:
Type: enhancement | Status: new
Priority: major | Milestone: sage-6.7
Component: symbolics | Resolution:
Keywords: | Merged in:
Authors: | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
Dependencies: | Stopgaps:
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Comment (by vdelecroix):
Replying to [comment:2 nbruin]:
> I'm not so sure we have to do more than document it. Obviously you
cannot expect substitutions to happen on any "equal" subexpression, since
that concept isn't well-defined.
I do not want to substitute "equal" subexpression but only identical ones.
And doing so, I want to consider 'a+c' as a unit of 'a+b+c+d' and 'a*c' as
a unit in 'a*b*c*d'. This is perhaps not desirable though.
> The thing is: `x+x^2` isn't a syntactical subunit of `x + x^2 + x^4` for
the internal representation, which is roughly `('+',x,('^',x,2))` versus
`('+',x,('^',x,2),('^',x,4))`
I know, and this is precisely the purpose of the ticket.
> You'll have to decide how much tricks are worthwhile to implement before
you just add the relation `y-(x^2+x)` and ask for elimination of x via
groebner bases.
Note that `x + y - (u + v)` does not exist. But I agree that there is an
ambiguous `+/-` issue (as far as the ticket description is concerned).
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Ticket URL: <http://trac.sagemath.org/ticket/18396#comment:3>
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