Fix LogLocator locating

dstansby · dstansby · commit 34d90dd3fa83 · 2021-09-25T15:24:15.000+01:00
diff --git a/lib/matplotlib/tests/test_colorbar.py b/lib/matplotlib/tests/test_colorbar.py
@@ -414,6 +414,7 @@ def test_colorbar_autotickslog():
         x = np.arange(-3.0, 4.001)
         y = np.arange(-4.0, 3.001)
         X, Y = np.meshgrid(x, y)
+        # Z ranges from -12 to 12
         Z = X * Y
         Z = Z[:-1, :-1]
         pcm = ax[0].pcolormesh(X, Y, 10**Z, norm=LogNorm())
@@ -423,12 +424,10 @@ def test_colorbar_autotickslog():
         pcm = ax[1].pcolormesh(X, Y, 10**Z, norm=LogNorm())
         cbar2 = fig.colorbar(pcm, ax=ax[1], extend='both',
                              orientation='vertical', shrink=0.4)
-        # note only -12 to +12 are visible
         np.testing.assert_almost_equal(cbar.ax.yaxis.get_ticklocs(),
-                                       10**np.arange(-16., 16.2, 4.))
-        # note only -24 to +24 are visible
+                                       10**np.arange(-12, 12.01, 4))
         np.testing.assert_almost_equal(cbar2.ax.yaxis.get_ticklocs(),
-                                       10**np.arange(-24., 25., 12.))
+                                       10**np.arange(-12, 12.01, 12))
 
 
 def test_colorbar_get_ticks():
@@ -515,6 +514,7 @@ def test_colorbar_log_minortick_labels():
 
 def test_colorbar_renorm():
     x, y = np.ogrid[-4:4:31j, -4:4:31j]
+    # z ranges from ~1.52e-9 to 1.2e5
     z = 120000*np.exp(-x**2 - y**2)
 
     fig, ax = plt.subplots()
@@ -529,7 +529,7 @@ def test_colorbar_renorm():
     norm = LogNorm(z.min(), z.max())
     im.set_norm(norm)
     np.testing.assert_allclose(cbar.ax.yaxis.get_majorticklocs(),
-                               np.logspace(-10, 7, 18))
+                               np.logspace(-8, 5, 14))
     # note that set_norm removes the FixedLocator...
     assert np.isclose(cbar.vmin, z.min())
     cbar.set_ticks([1, 2, 3])
@@ -564,7 +564,7 @@ def test_colorbar_format():
     im.set_norm(LogNorm(vmin=0.1, vmax=10))
     fig.canvas.draw()
     assert (cbar.ax.yaxis.get_ticklabels()[0].get_text() ==
-            r'$\mathdefault{10^{-2}}$')
+            r'$\mathdefault{10^{-1}}$')
 
 
 def test_colorbar_scale_reset():
diff --git a/lib/matplotlib/tests/test_ticker.py b/lib/matplotlib/tests/test_ticker.py
@@ -198,13 +198,11 @@ def test_basic(self):
         with pytest.raises(ValueError):
             loc.tick_values(0, 1000)
 
-        test_value = np.array([1.00000000e-05, 1.00000000e-03, 1.00000000e-01,
-                               1.00000000e+01, 1.00000000e+03, 1.00000000e+05,
-                               1.00000000e+07, 1.000000000e+09])
-        assert_almost_equal(loc.tick_values(0.001, 1.1e5), test_value)
+        test_value = np.array([1e-3, 1e-1, 1e1, 1e3, 1e5])
+        assert_almost_equal(loc.tick_values(0.9e-3, 1.1e5), test_value)
 
         loc = mticker.LogLocator(base=2)
-        test_value = np.array([0.5, 1., 2., 4., 8., 16., 32., 64., 128., 256.])
+        test_value = np.array([1, 2, 4, 8, 16, 32, 64])
         assert_almost_equal(loc.tick_values(1, 100), test_value)
 
     def test_switch_to_autolocator(self):
diff --git a/lib/matplotlib/ticker.py b/lib/matplotlib/ticker.py
@@ -2322,8 +2322,10 @@ def tick_values(self, vmin, vmax):
 
         if vmax < vmin:
             vmin, vmax = vmax, vmin
-        log_vmin = math.log(vmin) / math.log(b)
-        log_vmax = math.log(vmax) / math.log(b)
+        # Since base 10 is most common, use log10 here to minimise floating
+        # point errors when vmin/vmax is exactly on a decade
+        log_vmin = np.log10(vmin) / np.log10(b)
+        log_vmax = np.log10(vmax) / np.log10(b)
 
         numdec = math.floor(log_vmax) - math.ceil(log_vmin)
 
@@ -2342,7 +2344,7 @@ def tick_values(self, vmin, vmax):
         # Get decades between major ticks.
         stride = (max(math.ceil(numdec / (numticks - 1)), 1)
                   if mpl.rcParams['_internal.classic_mode'] else
-                  (numdec + 1) // numticks + 1)
+                  numdec // numticks)
 
         # if we have decided that the stride is as big or bigger than
         # the range, clip the stride back to the available range - 1
@@ -2355,9 +2357,9 @@ def tick_values(self, vmin, vmax):
         # whether we're a major or a minor locator.
         have_subs = len(subs) > 1 or (len(subs) == 1 and subs[0] != 1.0)
 
-        decades = np.arange(math.floor(log_vmin) - stride,
-                            math.ceil(log_vmax) + 2 * stride, stride)
-
+        decades = np.arange(math.ceil(log_vmin) - have_subs,
+                            math.floor(log_vmax) + 1,
+                            stride)
         if hasattr(self, '_transform'):
             ticklocs = self._transform.inverted().transform(decades)
             if have_subs:
@@ -2368,7 +2370,7 @@ def tick_values(self, vmin, vmax):
                     ticklocs = np.array([])
         else:
             if have_subs:
-                if stride == 1:
+                if stride == 1 and len(decades):
                     ticklocs = np.concatenate(
                         [subs * decade_start for decade_start in b ** decades])
                 else:
