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Noninteger Bases in mathtext sqrt · Issue #8665 · matplotlib/matplotlib · GitHub

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Noninteger Bases in mathtext sqrt #8665

Closed
Closed
Noninteger Bases in mathtext sqrt#8665
Labels
status: has patchpatch suggested, PR still neededtopic: text/mathtext
Milestone
v3.4.0

Description

ben-e-whitney
opened on May 25, 2017

Bug report

Bug summary
It appears that only integer sqrt bases are allowed by mathtext. The documentation does not list this limitation.

Code for reproduction

import matplotlib.pyplot as plt

fig = plt.figure()
axis = fig.add_subplot(1, 1, 1)
axis.plot(1, 1, label=r'$\sqrt[a]{{x}}$')
axis.legend()
plt.show()

Actual outcome
mathtext.Parser.parse raises a ValueError.

Expected outcome
The documentation states the following:

Radicals can be produced with the \sqrt[]{} command ... Any base can (optionally) be provided inside square brackets. Note that the base must be a simple expression, and can not contain layout commands such as fractions or sub/superscripts

In fact, it seems that only a (signed) integer literal is allowed. From mathtext.Parser.__init__:

p.sqrt          <<= Group(
                     Suppress(Literal(r"\sqrt"))
                   - ((Optional(p.lbracket + p.int_literal + p.rbracket, default=None)
                      + p.required_group)
                   | Error("Expected \sqrt{value}"))
                 )

It would be convenient if other bases were allowed. If that change cannot be made (or in the meantime), I think the documentation should be updated.

Matplotlib version

  • Operating System: Debian 9.0
  • Matplotlib Version: 2.0.0
  • Python Version: 3.5.3

I believe I installed Python from the python3.5 package in the stretch repository and Matplotlib from the python3-matplotlib package in the stretch repository, but I'm not sure.

Activity

  1. dstansby
    added
    Documentation
    topic: text
    on Dec 9, 2017
  2. anntzer
    added
    topic: text/mathtext
    and removed
    topic: text
    on Mar 22, 2019

  3. anntzer commented on Mar 25, 2019

    anntzer
    on Mar 25, 2019
    Contributor

    So

    diff --git i/lib/matplotlib/mathtext.py w/lib/matplotlib/mathtext.py
index ef7b8768f..c49a23ab1 100644
--- i/lib/matplotlib/mathtext.py
+++ w/lib/matplotlib/mathtext.py
@@ -2495,7 +2495,7 @@ class Parser(object):
 
         p.sqrt          <<= Group(
             Suppress(Literal(r"\sqrt"))
-            - ((Optional(p.lbracket + p.int_literal + p.rbracket, default=None)
+            - ((Optional(p.lbracket + p.token + p.rbracket, default=None)
                 + p.required_group)
                | Error("Expected \\sqrt{value}"))
         )
@@ -3231,7 +3231,7 @@ class Parser(object):
         if root is None:
             root = Box(check.width * 0.5, 0., 0.)
         else:
-            root = Hlist([Char(x, state) for x in root])
+            root = Hlist([root])
             root.shrink()
             root.shrink()

    makes $sqrt[{abc}]{123}$ work, but the extra braces in the brackets are needed. Unfortunately I haven't figured out how to make it work without the extra braces...

  4. anntzer
    removed
    Documentation
    on Nov 30, 2020

  5. anntzer commented on Nov 30, 2020

    anntzer
    on Nov 30, 2020
    Contributor

    OK, so the problem was that square brackets are actually not special most of the time, other than when parsing delimiters around the root base (and that's generically true in TeX as well, e.g. \sqrt[[]{a} just puts [ in the base position). So we need to explicitly exclude them (otherwise the parser just keeps chewing until the end when looking for the end of the base); looks like the following patch works:

    diff --git i/lib/matplotlib/_mathtext.py w/lib/matplotlib/_mathtext.py
index dd0305d4b..0e858574c 100644
--- i/lib/matplotlib/_mathtext.py
+++ w/lib/matplotlib/_mathtext.py
@@ -2158,7 +2158,8 @@ class Parser:
 
         p.sqrt <<= Group(
             Suppress(Literal(r"\sqrt"))
-            - ((Optional(p.lbracket + p.int_literal + p.rbracket, default=None)
+            - ((Group(Optional(
+                    p.lbracket + OneOrMore(~p.rbracket + p.token) + p.rbracket))
                 + p.required_group)
                | Error("Expected \\sqrt{value}"))
         )
@@ -2864,10 +2865,10 @@ class Parser:
 
         # Add the root and shift it upward so it is above the tick.
         # The value of 0.6 is a hard-coded hack ;)
-        if root is None:
+        if not root:
             root = Box(check.width * 0.5, 0., 0.)
         else:
-            root = Hlist([Char(x, state) for x in root])
+            root = Hlist(root)
             root.shrink()
             root.shrink()

    As always, brownie points for whoever turns this into a PR.

  6. anntzer
    added
    status: has patchpatch suggested, PR still needed
    on Nov 30, 2020

  7. anntzer commented on Jan 16, 2021

    anntzer
    on Jan 16, 2021
    Contributor

    Implemented in #19261, so the brownie mostly goes to @timhoffm but I'll keep a bit of it for myself (yum yum).

  8. anntzer
    closed this as completedon Jan 16, 2021
  9. QuLogic
    added this to the v3.4.0 milestone on Jan 18, 2021
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