Opened 8 years ago

Last modified 7 years ago

#11888 closed defect

Sage is missing the lambert_w function conversion from Maxima — at Initial Version

Reported by: benjaminfjones Owned by: burcin
Priority: minor Milestone: sage-5.1
Component: symbolics Keywords: lambert_w symbolics conversion maxima sd35.5 sd40.5
Cc: kcrisman, ktkohl Merged in:
Authors: Reviewers:
Report Upstream: N/A Work issues:
Branch: Commit:
Dependencies: Stopgaps:

Description

Maxima returns solutions to some exponential equations in terms of the lambert_w function. Sage is missing a conversion for this function:

sage: solve(e^(5*x)+x==0, x, to_poly_solve=True)
[x == -1/5*lambert_w(5)]
sage: S = solve(e^(5*x)+x==0, x, to_poly_solve=True)
sage: z = S[0].rhs()
sage: z
-1/5*lambert_w(5)
sage: N(z)
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)

/Users/jonesbe/sage/sage-4.7.2.alpha2/devel/sage-test/sage/<ipython console> in <module>()

/Users/jonesbe/sage/latest/local/lib/python2.6/site-packages/sage/misc/functional.pyc in numerical_approx(x, prec, digits)
   1264             prec = int((digits+1) * 3.32192) + 1
   1265     try:
-> 1266         return x._numerical_approx(prec)
   1267     except AttributeError:
   1268         from sage.rings.complex_double import is_ComplexDoubleElement

/Users/jonesbe/sage/latest/local/lib/python2.6/site-packages/sage/symbolic/expression.so in sage.symbolic.expression.Expression._numerical_approx (sage/symbolic/expression.cpp:17950)()

TypeError: cannot evaluate symbolic expression numerically
sage: lambert_w(5)
---------------------------------------------------------------------------
NameError                                 Traceback (most recent call last)

/Users/jonesbe/sage/sage-4.7.2.alpha2/devel/sage-test/sage/<ipython console> in <module>()

NameError: name 'lambert_w' is not defined
sage: 

mpmath can evaluate the lambert_w function, so it should be easy to add a new symbolic function to Sage that will fix this issue.

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