#11888: Sage is missing the lambert_w function
----------------------------------------------------------------+-----------
Reporter: benjaminfjones |
Owner: burcin
Type: defect |
Status: needs_review
Priority: minor |
Milestone: sage-5.0
Component: symbolics |
Resolution:
Keywords: lambert_w symbolics conversion maxima sd35.5 | Work
issues:
Report Upstream: N/A |
Reviewers: Keshav Kini, Karl-Dieter Crisman, Fredrik Johansson, Burcin Erocal
Authors: Benjamin Jones | Merged
in:
Dependencies: #12507 |
Stopgaps:
----------------------------------------------------------------+-----------
Description changed by benjaminfjones:
Old 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.
>
> ----
>
> Apply:
>
> * Patch at #12507
> * [attachment:trac_11888_v5.patch] to `$SAGE_ROOT/devel/sage`
New description:
Maxima returns solutions to some exponential equations in terms of the
`lambert_w` function. Sage is missing a conversion for this function:
{{{
sage: solve(e^(5*x)+x==0, x, to_poly_solve=True)
[x == -1/5*lambert_w(5)]
sage: S = solve(e^(5*x)+x==0, x, to_poly_solve=True)
sage: z = S[0].rhs()
sage: z
-1/5*lambert_w(5)
sage: N(z)
---------------------------------------------------------------------------
TypeError Traceback (most recent call
last)
/Users/jonesbe/sage/sage-4.7.2.alpha2/devel/sage-test/sage/<ipython
console> in <module>()
/Users/jonesbe/sage/latest/local/lib/python2.6/site-
packages/sage/misc/functional.pyc in numerical_approx(x, prec, digits)
1264 prec = int((digits+1) * 3.32192) + 1
1265 try:
-> 1266 return x._numerical_approx(prec)
1267 except AttributeError:
1268 from sage.rings.complex_double import
is_ComplexDoubleElement
/Users/jonesbe/sage/latest/local/lib/python2.6/site-
packages/sage/symbolic/expression.so in
sage.symbolic.expression.Expression._numerical_approx
(sage/symbolic/expression.cpp:17950)()
TypeError: cannot evaluate symbolic expression numerically
sage: lambert_w(5)
---------------------------------------------------------------------------
NameError Traceback (most recent call
last)
/Users/jonesbe/sage/sage-4.7.2.alpha2/devel/sage-test/sage/<ipython
console> in <module>()
NameError: name 'lambert_w' is not defined
sage:
}}}
`mpmath` can evaluate the `lambert_w` function, so it should be easy to
add a new symbolic function to Sage that will fix this issue.
----
Apply:
* [attachment:trac_11888_v7.patch] to `$SAGE_ROOT/devel/sage`
--
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/11888#comment:39>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
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