Status: Accepted
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Labels: Type-Defect Priority-Medium Milestone-Release0.7.0
New issue 1520 by fab...@fseoane.net: Inconsistency in subs
http://code.google.com/p/sympy/issues/detail?id=1520
I think I found some inconsistencies in the behavior of .subs. For example,
why doesn't the fo
Issue 1520: Inconsistency in subs
http://code.google.com/p/sympy/issues/detail?id=1520
This issue is now blocking issue 1358.
See http://code.google.com/p/sympy/issues/detail?id=1358
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Comment #1 on issue 1520 by wflynny: Inconsistency in subs
http://code.google.com/p/sympy/issues/detail?id=1520
As you said, Mathematica does not match non-existent symbols.
In[1]:= x*y /. (2*x) -> 2
Out[1]= x y
In[4]:= x*y /. 2 x -> 2
Out[4]= x y
Neither does Maxima:
(%i4) subst(2,2*x,x*y);
Comment #2 on issue 1520 by ondrej.certik: Inconsistency in subs
http://code.google.com/p/sympy/issues/detail?id=1520
Yes, I agree subs should be only substituting what is actually in the
expression.
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Comment #3 on issue 1520 by wflynny: Inconsistency in subs
http://code.google.com/p/sympy/issues/detail?id=1520
So it's clear that
(x*y).subs(2*x,1)
return x*y.
But how about expressions like 3*x*y instead of x*y. Should this return
3/2*y or not
do the subs? I guess what I am asking is, shoul
Comment #4 on issue 1520 by asmeurer: Inconsistency in subs
http://code.google.com/p/sympy/issues/detail?id=1520
Maple has two commands, subs, which does strict substitution (has to appear
exactly in the expression, neither
3*x*y or 4*x*y would work), and algsubs, which does algebraic substitu
Comment #5 on issue 1520 by wflynny: Inconsistency in subs
http://code.google.com/p/sympy/issues/detail?id=1520
Personally, I think that subs should implement the old_coeff | expr_coeff
determination. We could implement a *kwargs system I guess to get the
algsubs type
functionality working.
-
Issue 1520: Inconsistency in subs
http://code.google.com/p/sympy/issues/detail?id=1520
This issue is no longer blocking issue 1358.
See http://code.google.com/p/sympy/issues/detail?id=1358
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Issue 1520: Inconsistency in subs
http://code.google.com/p/sympy/issues/detail?id=1520
This issue is no longer blocking issue 1358.
See http://code.google.com/p/sympy/issues/detail?id=1358
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Issue 1520: Inconsistency in subs
http://code.google.com/p/sympy/issues/detail?id=1520
This issue is no longer blocking issue 1358.
See http://code.google.com/p/sympy/issues/detail?id=1358
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Issue 1520: Inconsistency in subs
http://code.google.com/p/sympy/issues/detail?id=1520
This issue is no longer blocking issue 1358.
See http://code.google.com/p/sympy/issues/detail?id=1358
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Issue 1520: Inconsistency in subs
http://code.google.com/p/sympy/issues/detail?id=1520
This issue is no longer blocking issue 1358.
See http://code.google.com/p/sympy/issues/detail?id=1358
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Issue 1520: Inconsistency in subs
http://code.google.com/p/sympy/issues/detail?id=1520
This issue is no longer blocking issue 1358.
See http://code.google.com/p/sympy/issues/detail?id=1358
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Issue 1520: Inconsistency in subs
http://code.google.com/p/sympy/issues/detail?id=1520
This issue is no longer blocking issue 1358.
See http://code.google.com/p/sympy/issues/detail?id=1358
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Updates:
Status: Fixed
Comment #11 on issue 1520 by ronan.l...@gmail.com: Inconsistency in subs
http://code.google.com/p/sympy/issues/detail?id=1520
The inconsistency described in the OP doesn't exist any more, so we can
consider this fixed.
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Labels: Matching
Comment #7 on issue 1520 by ronan.l...@gmail.com: Inconsistency in subs
http://code.google.com/p/sympy/issues/detail?id=1520
In my branch "pattern-wip-091202" (see issue 1736), there's a preliminary
implementation of something quite like Maple's subs.
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Issue 1520: Inconsistency in subs
http://code.google.com/p/sympy/issues/detail?id=1520
This issue is no longer blocking issue 1358.
See http://code.google.com/p/sympy/issues/detail?id=1358
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Updates:
Labels: -Milestone-Release0.7.0 Milestone-Release0.7.1
Comment #8 on issue 1520 by asmeurer: Inconsistency in subs
http://code.google.com/p/sympy/issues/detail?id=1520
See also issue 2027.
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Comment #9 on issue 1520 by smi...@gmail.com: Inconsistency in subs
http://code.google.com/p/sympy/issues/detail?id=1520
subs is more constistent now and only does the substitution if old is
multiplicatively extractable from expr.
h[2] >>> x.subs(2*x, 1)
x
h[3] >>> (y*x).subs(2*x
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