typo in lambert_w._print_latex_()

[rwst]

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()

CC: @kcrisman

Component: symbolics

Author: Frédéric Chapoton

Branch/Commit: a87b149

Reviewer: Ralf Stephan

Issue created by migration from https://trac.sagemath.org/ticket/19336

[videlec]

comment:3

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

[fchapoton]

Commit: 6a9b8ea

[fchapoton]

Branch: public/19336

[fchapoton]

New commits:

6a9b8ea

trac #19336 fixing custom latex of Lambert W function

[fchapoton]

Author: Frédéric Chapoton

[nbruin]

comment:5

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]

comment:6

Replying to @videlec:

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.