ENH: restore default ability to label some minor log ticks.

efiring · efiring · commit 129a32beb698 · 2016-11-06T18:44:22.000-10:00
This partly restores the functionality that was added in PR #5161 and partly removed in #7000. The "partly" is because now the labeling of minor log ticks is turned on only when numdecs (the axis range in powers of the log base) is less than or equal to one, rather than 3. This also fixes a bug that was causing double labeling with a base of 2; minor ticks were coinciding with major ticks, and both were being labeled.
diff --git a/examples/pylab_examples/log_demo.py b/examples/pylab_examples/log_demo.py
@@ -21,7 +21,7 @@
 plt.subplot(223)
 plt.loglog(t, 20*np.exp(-t/10.0), basex=2)
 plt.grid(True)
-plt.title('loglog base 4 on x')
+plt.title('loglog base 2 on x')
 
 # with errorbars: clip non-positive values
 ax = plt.subplot(224)
diff --git a/lib/matplotlib/scale.py b/lib/matplotlib/scale.py
@@ -306,7 +306,7 @@ def set_default_locators_and_formatters(self, axis):
         axis.set_major_locator(LogLocator(self.base))
         axis.set_major_formatter(LogFormatterSciNotation(self.base))
         axis.set_minor_locator(LogLocator(self.base, self.subs))
-        axis.set_minor_formatter(NullFormatter())
+        axis.set_minor_formatter(LogFormatterSciNotation(self.base, self.subs))
 
     def get_transform(self):
         """
diff --git a/lib/matplotlib/tests/test_ticker.py b/lib/matplotlib/tests/test_ticker.py
@@ -250,13 +250,16 @@ def test_LogFormatter_sublabel():
     assert np.all(show_major_labels)
     _sub_labels(ax.xaxis, subs=[])
 
-    # axis range at 2 to 3 decades, label sub 3
+    # For the next two, if the numdec threshold in LogFormatter.set_locs
+    # were 3, then the label sub would be 3 for 2-3 decades and (2,5)
+    # for 1-2 decades.  With a threshold of 1, subs are not labeled.
+    # axis range at 2 to 3 decades
     ax.set_xlim(1, 800)
-    _sub_labels(ax.xaxis, subs=[3])
+    _sub_labels(ax.xaxis, subs=[])
 
-    # axis range at 1 to 2 decades, label subs 2 and 5
+    # axis range at 1 to 2 decades
     ax.set_xlim(1, 80)
-    _sub_labels(ax.xaxis, subs=[2, 5])
+    _sub_labels(ax.xaxis, subs=[])
 
     # axis range at 0 to 1 decades, label subs 2, 3, 6
     ax.set_xlim(1, 8)
diff --git a/lib/matplotlib/ticker.py b/lib/matplotlib/ticker.py
@@ -853,7 +853,7 @@ def set_locs(self, locs):
             vmax = math.log(vmax) / math.log(b)
             numdec = abs(vmax - vmin)
 
-        if numdec > 3:
+        if numdec > 1:
             # Label only bases
             self.sublabel = set((1,))
         else:
@@ -1857,10 +1857,10 @@ def tick_values(self, vmin, vmax):
 
         numdec = math.floor(vmax) - math.ceil(vmin)
 
-        if self._subs is None:  # autosub
-            if numdec > 10:
-                subs = np.array([1.0])
-            elif numdec > 6:
+        if self._subs is None:  # autosub for minor ticks
+            if numdec > 10 or b < 3:
+                return np.array([])  # no minor ticks
+            elif numdec > 5 and b >= 6:
                 subs = np.arange(2.0, b, 2.0)
             else:
                 subs = np.arange(2.0, b)
