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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