Opened 3 years ago

Last modified 3 years ago

#24255 new defect

Fix Expression subclasses coercion into SR — at Version 4

Reported by: rws Owned by:
Priority: major Milestone: sage-8.2
Component: symbolics Keywords:
Cc: Merged in:
Authors: Reviewers:
Report Upstream: N/A Work issues:
Branch: Commit:
Dependencies: Stopgaps:

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Description (last modified by rws)

There is a long-standing problem with substitution in that some substitutions do not work when given as equality but do work when given as dictionary. 

sage: (x*pi).subs(x*pi==e)
x*pi
sage: (x*pi).subs({x*pi:e})
e

sage: s = x.series(x,2); s
1*x + Order(x^2)

It looks like that in some cases the conversion to dict switches lhs and rhs of the equation and this is because of such behaviour: 

sage: x*pi==e
e == pi*x
sage: x == s
1*x + Order(x^2) == x

The problem is that constants/series are subclasses of Expression and are not coerced/converted immediately into Expression: 

sage: SR(e)
e
sage: type(_)
<type 'sage.symbolic.constants_c.E'>
sage: e+1-1
e
sage: type(_)
<type 'sage.symbolic.expression.Expression'>

Change History (4)

comment:1 Changed 3 years ago by rws

  • Description modified (diff)

comment:2 Changed 3 years ago by rws

  • Description modified (diff)
  • Summary changed from Fix substitution with pattern given as equation to Fix constants coercion into SR

comment:3 Changed 3 years ago by rws

  • Description modified (diff)
  • Summary changed from Fix constants coercion into SR to Fix constant e coercion into SR

comment:4 Changed 3 years ago by rws

  • Description modified (diff)
  • Summary changed from Fix constant e coercion into SR to Fix Expression subclasses coercion into SR
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