matplotlib · dstansby · May 24, 2019 · May 24, 2019 · Jun 5, 2019
diff --git a/lib/matplotlib/tests/baseline_images/test_axes/symlog.pdf b/lib/matplotlib/tests/baseline_images/test_axes/symlog.pdf
diff --git a/lib/matplotlib/tests/baseline_images/test_axes/symlog2.pdf b/lib/matplotlib/tests/baseline_images/test_axes/symlog2.pdf
diff --git a/lib/matplotlib/ticker.py b/lib/matplotlib/ticker.py
@@ -2408,33 +2408,24 @@ def tick_values(self, vmin, vmax):
         #
         # "simple" mode is when the range falls entirely within (-t,
         # t) -- it should just display (vmin, 0, vmax)
+        if -linthresh < vmin < vmax < linthresh:
+            return [vmin, vmax]
 
-        # Determine which of the three ranges we have
-        has_a = has_b = has_c = False
-        if vmin < -linthresh:
-            has_a = True
-            if vmax > -linthresh:
-                has_b = True
-                if vmax > linthresh:
-                    has_c = True
-        elif vmin < 0:
-            if vmax > 0:
-                has_b = True
-                if vmax > linthresh:
-                    has_c = True
-            else:
-                return [vmin, vmax]
-        elif vmin < linthresh:
-            if vmax > linthresh:
-                has_b = True
-                has_c = True
-            else:
-                return [vmin, vmax]
+        has_a = (vmin < -linthresh)
+        has_c = (vmax > linthresh)
+
+        if (has_a and vmax > -linthresh) or (has_c and vmin < linthresh):
+            has_b = True
         else:
-            has_c = True
+            has_b = False
 
         def get_log_range(lo, hi):
-            lo = np.floor(np.log(lo) / np.log(base))
+            """
+            Get the first integer exponents above *lo* and *hi*. These are
+            chosen to be above in both cases to avoid encroaching range b for
+            lo, and to extend out of ranges a or c for hi.
+            """
+            lo = np.ceil(np.log(lo) / np.log(base))
             hi = np.ceil(np.log(hi) / np.log(base))
             return lo, hi