matplotlib · timhoffm · Oct 6, 2022 · Aug 22, 2022 · Aug 22, 2022
diff --git a/lib/matplotlib/_mathtext.py b/lib/matplotlib/_mathtext.py
@@ -475,6 +475,14 @@ class UnicodeFonts(TruetypeFonts):
    symbol can not be found in the font.
    """

+    # Some glyphs are not present in the `cmr10` font, and must be brought in
+    # from `cmsy10`. Map the Unicode indices of those glyphs to the indices at
+    # which they are found in `cmsy10`.
+    _cmr10_substitutions = {
+        0x00D7: 0x00A3,  # Multiplication sign.
+        0x2212: 0x00A1,  # Minus sign.
+    }
+
    def __init__(self, *args, **kwargs):
        # This must come first so the backend's owner is set correctly
        fallback_rc = mpl.rcParams['mathtext.fallback']
@@ -541,11 +549,11 @@ def _get_glyph(self, fontname, font_class, sym):
            found_symbol = False
            font = self._get_font(new_fontname)
            if font is not None:
-                if font.family_name == "cmr10" and uniindex == 0x2212:
-                    # minus sign exists in cmsy10 (not cmr10)
+                if (uniindex in self._cmr10_substitutions
+                        and font.family_name == "cmr10"):
                    font = get_font(
                        cbook._get_data_path("fonts/ttf/cmsy10.ttf"))
-                    uniindex = 0xa1
+                    uniindex = self._cmr10_substitutions[uniindex]
                glyphindex = font.get_char_index(uniindex)
                if glyphindex != 0:
                    found_symbol = True

diff --git a/lib/matplotlib/tests/test_ticker.py b/lib/matplotlib/tests/test_ticker.py
@@ -1,6 +1,7 @@
 from contextlib import nullcontext
 import itertools
 import locale
+import logging
 import re

 import numpy as np
@@ -725,6 +726,24 @@ def test_mathtext_ticks(self):
            ax.set_xticks([-1, 0, 1])
            fig.canvas.draw()

+    def test_cmr10_substitutions(self, caplog):
+        mpl.rcParams.update({
+            'font.family': 'cmr10',
+            'mathtext.fontset': 'cm',
+            'axes.formatter.use_mathtext': True,
+        })
+
+        # Test that it does not log a warning about missing glyphs.
+        with caplog.at_level(logging.WARNING, logger='matplotlib.mathtext'):
+            fig, ax = plt.subplots()
+            ax.plot([-0.03, 0.05], [40, 0.05])
+            ax.set_yscale('log')
+            yticks = [0.02, 0.3, 4, 50]
+            formatter = mticker.LogFormatterSciNotation()
+            ax.set_yticks(yticks, map(formatter, yticks))
+            fig.canvas.draw()
+            assert not caplog.text
+
    def test_empty_locs(self):
        sf = mticker.ScalarFormatter()
        sf.set_locs([])