Opened 4 years ago
Closed 4 years ago
#22525 closed defect (fixed)
Improper expressions from SR(string)
Reported by:  rws  Owned by:  

Priority:  major  Milestone:  sage8.1 
Component:  symbolics  Keywords:  FriCAS 
Cc:  mantepse  Merged in:  
Authors:  Frédéric Chapoton  Reviewers:  Martin Rubey 
Report Upstream:  N/A  Work issues:  
Branch:  f9b0635 (Commits, GitHub, GitLab)  Commit:  f9b0635bc6f56595c16c4db99ccc6733270dc2b7 
Dependencies:  Stopgaps: 
Description (last modified by )
Strings are not translated into proper Sage expressions for some functions:
sage: SR("sin(x)") sin(x) sage: type(_.operator()) <class 'sage.functions.trig.Function_sin'> sage: SR("arcsin(x)") arcsin(x) sage: type(_.operator()) <class 'sage.functions.trig.Function_arcsin'> sage: SR("asin(x)") asin(x) sage: type(_.operator()) <class 'sage.symbolic.function_factory.NewSymbolicFunction'>
Previous ticket description:
sage: integrate(((13*x)^(1/2)*(1+3*x)^(1/2)),x,algorithm='fricas') 2/3*atan(1/3*(sqrt(3*x  1)*sqrt(3*x  1)  1)/x) sage: _.subs(x==.1) 2/3*atan(6.51313067138982 + 3.89412863198815e16*I) sage: _.n()  TypeError Traceback (most recent call last) <ipythoninput29875d0b089ddd> in <module>() > 1 _.n() /home/ralf/sage/src/sage/structure/element.pyx in sage.structure.element.Element.n (build/cythonized/sage/structure/element.c:7987)() 836 0.666666666666667 837 """ > 838 return self.numerical_approx(prec, digits, algorithm) 839 840 N = deprecated_function_alias(13055, n) /home/ralf/sage/src/sage/symbolic/expression.pyx in sage.symbolic.expression.Expression.numerical_approx (build/cythonized/sage/symbolic/expression.cpp:33844)() 5566 res = x.pyobject() 5567 else: > 5568 raise TypeError("cannot evaluate symbolic expression numerically") 5569 5570 # Important  the we get might not be a valid output for numerical_approx in TypeError: cannot evaluate symbolic expression numerically
Already the second command should have evaluated to a floating point value.
Change History (21)
comment:1 Changed 4 years ago by
 Cc mantepse added
 Keywords FriCAS added
comment:2 Changed 4 years ago by
I don't quite get what's happening. Is there something wrong with my "a"?
sage: [f(x)._fricas_().sage().subs(x=1.0) for f in [sin, cos, sec, csc, cot, tan, asin, acos, ....: atan, acot, acsc, asec, arcsin, arccos, arctan, arccot, arccsc, arcsec]] [0.841470984807897, 0.540302305868140, 1.85081571768093, 1.18839510577812, 0.642092615934331, 1.55740772465490, asin(1.00000000000000), acos(1.00000000000000), atan(1.00000000000000), acot(1.00000000000000), acsc(1.00000000000000), asec(1.00000000000000), asin(1.00000000000000), acos(1.00000000000000), atan(1.00000000000000), acot(1.00000000000000), acsc(1.00000000000000), asec(1.00000000000000)] sage: [f(x)._fricas_().sage().subs(x=1.0) for f in [tanh, sinh, cosh, coth, sech, csch, asinh, ....: acosh, atanh, acoth, asech, acsch, arcsinh, arccosh, arctanh, arccoth, arcsech, arccsch ....: ]] [0.761594155955765, 1.17520119364380, 1.54308063481524, 1.31303528549933, 0.648054273663885, 0.850918128239322, asinh(1.00000000000000), acosh(1.00000000000000), atanh(1.00000000000000), acoth(1.00000000000000), asech(1.00000000000000), acsch(1.00000000000000), asinh(1.00000000000000), acosh(1.00000000000000), atanh(1.00000000000000), acoth(1.00000000000000), asech(1.00000000000000), acsch(1.00000000000000)]
comment:3 Changed 4 years ago by
I just learned:
sage: type(fricas(atan(x)).sage().operator()) <class 'sage.symbolic.function_factory.NewSymbolicFunction'> sage: type(atan(x).operator()) <class 'sage.functions.trig.Function_arctan'> sage: type(fricas(sin(x)).sage().operator()) <class 'sage.functions.trig.Function_sin'>
but I do not know where this NewSymbolicFunction
thing comes from, and why it only appears for atan
.
comment:4 Changed 4 years ago by
 Description modified (diff)
 Keywords FriCAS removed
 Summary changed from Improper expressions from FriCAS interface to Improper expressions from SR(string)
Interesting. It's the conversion via SR(string)
.
comment:5 Changed 4 years ago by
 Description modified (diff)
In calculus/calculus.py:symbolic_expression_from_string()
the arc
versions are recognized but not the a
versions.
comment:6 Changed 4 years ago by
However if I put these into the global _augmented
dict (as string/function pairs) the dict will be empty when doctesting via sage tp
. Can someone explain this to a Python amateur?
comment:7 Changed 4 years ago by
not sure whether the following is helpful:
sage: from sage.libs.pynac.pynac import symbol_table sage: type(symbol_table["functions"]["sin"]) <class 'sage.functions.trig.Function_sin'> sage: type(symbol_table["functions"]["asin"]) <class 'sage.symbolic.function_factory.NewSymbolicFunction'> sage: type(symbol_table["functions"]["arcsin"]) <class 'sage.functions.trig.Function_arcsin'>
comment:8 Changed 4 years ago by
Sorry, mistake: in a fresh session we have
sage: from sage.libs.pynac.pynac import symbol_table sage: type(symbol_table["functions"]["asin"])  KeyError Traceback (most recent call last) <ipythoninput395eddacf035c> in <module>() > 1 type(symbol_table["functions"]["asin"]) KeyError: 'asin'
comment:9 Changed 4 years ago by
Is it possible that SR("asin")
, SR("atan")
, etc. actually are supposed to fail?
I don't know how the "conversion" machinery is supposed to work, but symbol_table["fricas"]
does contain the correct translations. For example:
sage: from sage.libs.pynac.pynac import symbol_table sage: symbol_table["fricas"]["asin"] arcsin sage: type(_) <class 'sage.functions.trig.Function_arcsin'>
Also, it does seem to be a problem with the fricas interface:
sage: type(maxima("asin(x)").sage().operator()) <class 'sage.functions.trig.Function_arcsin'> sage: type(fricas("asin(x)").sage().operator()) <class 'sage.symbolic.function_factory.NewSymbolicFunction'>
In fact, maxima_abstract.py:_sage_
contains (skipping the docstring)
def _sage_(self): """ ... """ import sage.calculus.calculus as calculus return calculus.symbolic_expression_from_maxima_string(self.name(), maxima=self.parent())
which looks more plausible than the fricas.py
counterpart (which I wrote...):
from sage.symbolic.ring import SR s = unparsed_InputForm replacements = [('pi()', 'pi '), ('::Symbol', ' ')] for old, new in replacements: s = s.replace(old, new) try: return SR(s) except TypeError: raise NotImplementedError("The translation of the FriCAS Expression %s to sage is not yet implemented." %s)
comment:10 Changed 4 years ago by
I'm now pretty much convinced that it is wrongdoing of the FriCAS interface. An essential step in symbolic_expression_from_maxima_string
is to replace all known functions with their sage equivalent, using symbol_table
.
So, we should do the following: rewrite fricas._sage_expression
, which currently takes the unparsed InputForm
of a FriCAS Expression Integer
or OrderedCompletion Expression Integer
object as follows:
 input should be the
InputForm
, instead of theunparsed InputForm
, which is essentially a nested list of the form(function arg1 arg2 ...)
(lisp syntax)  replace function by its sage equivalent, and recurse.
I am unlikely to do that.
comment:11 Changed 4 years ago by
 Keywords FriCAS added
comment:12 Changed 4 years ago by
I think your analysis didn't consider the fact that return SR(s)
in fricas.py
calls symbolic_expression_from_string
and therefore symbolic_expression_from_string
would be the code to fix.
comment:13 Changed 4 years ago by
Yes, but it shouldn't. symbolic_expression_from_string
hopes for expressions in terms of the dictionary symbol_table["functions"]
, not symbol_table["fricas"]
. I didn't know about symbol_table
when I coded the interface.
comment:14 Changed 4 years ago by
 Branch set to public/22525
 Commit set to 77753048d3778fc4c286d1ed689e0502fc58e2d4
 Status changed from new to needs_info
Here is a tentative of enhancement.
New commits:
7775304  trac 22525 better conversion from fricas expressions

comment:15 Changed 4 years ago by
 Milestone changed from sage7.6 to sage8.1
comment:16 Changed 4 years ago by
 Commit changed from 77753048d3778fc4c286d1ed689e0502fc58e2d4 to f9b0635bc6f56595c16c4db99ccc6733270dc2b7
Branch pushed to git repo; I updated commit sha1. New commits:
f9b0635  add a test

comment:17 Changed 4 years ago by
This looks great! I added a test checking that we can use it to compute numerical values, which is probably the most interesting part of the fix.
Unfortunately, I have to recompile almost from scratch. I'll set it to positive review afterwards.
comment:18 Changed 4 years ago by
 Reviewers set to Martin Rubey
 Status changed from needs_info to needs_review
comment:19 Changed 4 years ago by
comment:21 Changed 4 years ago by
 Branch changed from public/22525 to f9b0635bc6f56595c16c4db99ccc6733270dc2b7
 Resolution set to fixed
 Status changed from positive_review to closed
A simpler way to see the bug: