typo in lambert_w._print_latex_()

[rws]

From ​https://groups.google.com/forum/?hl=en#!topic/sage-support/bjrk5270wEE

LaTeX output is defect.

this is probably

diff --git a/src/sage/functions/log.py b/src/sage/functions/log.py
index cc59437..17241ad 100644
--- a/src/sage/functions/log.py
+++ b/src/sage/functions/log.py
@@ -766,8 +766,8 @@ class Function_lambert_w(BuiltinFunction):
             \operatorname{W_{1}}(x)
         """
         if n == 0:
-            return r"\operatorname{W_0}(%s)" % z
+            return r"\operatorname{W_0}({%s})" % z
         else:
-            return r"\operatorname{W_{%s}}(%s)" % (n, z)
+            return r"\operatorname{W_{%s}}({%s})" % (n, z)
 
 lambert_w = Function_lambert_w()

[vdelecroix]

What is the point of having a separate n==0 case?

[chapoton]

New commits:

​6a9b8ea

trac #19336 fixing custom latex of Lambert W function

[nbruin]

Inserting the braces is a nice start, but it doesn't fix the entire problem. Compare:

sage: var("a1,a2")
(a1, a2)
sage:  latex(log( (a1+a1*a2)/a2))
\log\left(\frac{a_{1} a_{2} + a_{1}}{a_{2}}\right)
sage:  latex(lambert_w( (a1+a1*a2)/a2))
\operatorname{W_0}({(a1*a2 + a1)/a2})

As you can see a function like "log" processes its arguments further for latex. Just inserting braces doesn't cut it.

In bessel.py, the latex-ing of the arguments is done explicitly:

    def _print_latex_(self, n, z):
        return r"\operatorname{J_{%s}}(%s)" % (latex(n), latex(z))

That's probably the thing to do for lambert_w too.

[nbruin]

Replying to vdelecroix:

What is the point of having a separate n==0 case?

There's a case split for normal printing, suppressing a zero argument:

sage: lambert_w(0,x)
lambert_w(x)
sage: lambert_w(1,x)
lambert_w(1, x)

Possibly the same was done for latex at some point. I agree that with the current code, the case split can be removed in the latex code.

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​b7620a2	Merge branch 'public/19336' into 6.9.rc3
​70d9d51	trac #19336 latex of lambert_w again, plus a few local enhancements

[chapoton]

Here is a version with latex applied to the argument.

I have also taken the opportunity to enhance the link with maxima, which now has the other branches of LambertW.

[chapoton]

ping ?

[rws]

Could you please add doctests for the Maxima additions? When done you can set positive since patchbot is already ok with it.

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​d7c946e	Merge branch 'public/19336' into 6.9
​a87b149	trac #19336 some more doctest for maxima lambert_w

[chapoton]

ok, I have added some doctests, hopefully corresponding to what you asked.

I set to positive review.