Opened 8 years ago
Closed 8 years ago
#553 closed enhancement (fixed)
[with patch, positive review] calling of symbolic expressions is sometimes ridiculous
Reported by: | was | Owned by: | mhansen |
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Priority: | major | Milestone: | sage-2.9 |
Component: | calculus | Keywords: | |
Cc: | Merged in: | ||
Authors: | Reviewers: | ||
Report Upstream: | Work issues: | ||
Branch: | Commit: | ||
Dependencies: | Stopgaps: |
Description
The input should be f = x^(1/9) + (2^(8/9) - 2^(1/9))*(x - 1) - x^(8/9) Note that * before (x-1). That your input was accepted is an indication that SAGE should be more restrictive with what it allows. What's happening is that (2^(8/9) - 2^(1/9)) is parsed as a symbolic expression (a constant function), and then 2^(8/9) - 2^(1/9))(x - 1) is the value of that constant function at x-1. Yep, that this is allowed is ridiculous, and should be changed (I've filed a bug report).
Attachments (3)
Change History (13)
Changed 8 years ago by mhansen
comment:1 Changed 8 years ago by mhansen
- Owner changed from was to mhansen
comment:2 Changed 8 years ago by was
- Resolution set to fixed
- Status changed from new to closed
comment:3 Changed 8 years ago by was
- Resolution fixed deleted
- Status changed from closed to reopened
This patch doesn't fix the problem at all. If you apply it the above example
doesn't raise an error. In fact, it's a patch against named substitutions, which
should *always* be allowed. So this was totally wrong.
I'm worried actually that the expense of determining whether or not an expression
is too costly. The only reasonable fix is to completely ban calling "non-callable"
symbolic expressions without an explicit substitution. doing this is a lot more
work though.
comment:4 Changed 8 years ago by was
- Milestone changed from sage-2.9 to sage-3
- Type changed from defect to enhancement
comment:5 Changed 8 years ago by mabshoff
- Milestone changed from sage-feature to sage-2.8.13
- Summary changed from calling of symbolic expressions is sometimes ridiculous to [with patch] calling of symbolic expressions is sometimes ridiculous
comment:6 Changed 8 years ago by mabshoff
- Summary changed from [with patch] calling of symbolic expressions is sometimes ridiculous to [with broken patch] calling of symbolic expressions is sometimes ridiculous
comment:7 Changed 8 years ago by mhansen
I think the best way to go about doing this is to add a number_of_arguments() to SymbolicExpressions?:
sage: sin.number_of_arguments() 1 sage: (sin+1).number_of_arguments() 1 sage: (sin+x).number_of_arguments() 1 sage: (sin+x+y).number_of_arguments() 2 sage: (2^(8/9)-2^(1/9)).number_of_arguments() 0
Changed 8 years ago by mhansen
comment:8 Changed 8 years ago by mhansen
- Summary changed from [with broken patch] calling of symbolic expressions is sometimes ridiculous to [with patch] calling of symbolic expressions is sometimes ridiculous
I've put up a new patch.
comment:9 Changed 8 years ago by was
- Summary changed from [with patch] calling of symbolic expressions is sometimes ridiculous to [with patch, positive review] calling of symbolic expressions is sometimes ridiculous
comment:10 Changed 8 years ago by mabshoff
- Resolution set to fixed
- Status changed from reopened to closed
Merged in 2.9.rc0.
I attached a patch which throws an error when trying to substitute into a constant expression.
It can be overridden by passing a substitute=True parameter to call.
All doc tests pass with it.