#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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Description changed by vdelecroix:
Old description:
> Sage is not able to identify partial sum in a substitution
> {{{
> sage: var('x,y,z')
> sage: f = x^4 + x^2 + x
> sage: f.subs(x^4 + x^2 == y)
> x^4 + x^2 + x
> }}}
> Similarly with products
> {{{
> sage: f = x * cos(x) * sin(x)
> sage: f.subs( cos(x) * sin(x) == y)
> x*cos(x)*sin(x)
> }}}
>
> As mentioned in the doc, this is the same behavior as in Maple but differ
> from Mathematica. We should be clearer on the semantic of `substitute`
> and potentially implement partial sum and product substitutions.
New description:
Sage is not able to identify partial sum in a substitution
{{{
sage: var('x,y')
sage: f = x + x^2 + x^4
sage: f.subs(x^2 == y) # one term is fine
x^4 + x + y
sage: f.subs(x + x^2 == y) # partial sum does not work
x^4 + x^2 + x
sage: f.subs(x + x^2 + x^4 == y) # whole sum is fine
y
}}}
Similarly with products
{{{
sage: f = x * cos(x) * sin(x)
sage: f.subs( cos(x) * sin(x) == y)
x*cos(x)*sin(x)
}}}
As mentioned in the doc, this is the same behavior as in Maple but differ
from Mathematica. We should be clearer on the semantic of `substitute` and
potentially implement partial sum and product substitutions.
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Ticket URL: <http://trac.sagemath.org/ticket/18396#comment:1>
Sage <http://www.sagemath.org>
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and MATLAB
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