Merge pull request #3612 from nhmc/minor_tick_fix

BUG : fix minor tick placement

Merging by hand as I added a testing clean up commit on top of
the original branch.

lib/matplotlib/tests/test_ticker.py

@@ -7,9 +7,9 @@
 from numpy.testing import assert_almost_equal
 import numpy as np
 import matplotlib
-
+import matplotlib.pyplot as plt
 import matplotlib.ticker as mticker
-
+from matplotlib.testing.decorators import cleanup
 
 def test_MaxNLocator():
     loc = mticker.MaxNLocator(nbins=5)
@@ -36,6 +36,17 @@ def test_MultipleLocator():
     assert_almost_equal(loc.tick_values(-7, 10), test_value)
 
 
+@cleanup
+def test_AutoMinorLocator():
+    fig, ax = plt.subplots()
+    ax.set_xlim(0, 1.39)
+    ax.minorticks_on()
+    test_value = np.array([0.05, 0.1, 0.15, 0.25, 0.3, 0.35, 0.45,
+                           0.5, 0.55, 0.65, 0.7, 0.75, 0.85, 0.9,
+                           0.95, 1, 1.05, 1.1, 1.15, 1.25, 1.3, 1.35])
+    assert_almost_equal(ax.xaxis.get_ticklocs(minor=True), test_value)
+
+
 def test_LogLocator():
     loc = mticker.LogLocator(numticks=5)
 

lib/matplotlib/ticker.py

@@ -1747,8 +1747,8 @@ def __call__(self):
 
         if len(majorlocs) > 0:
             t0 = majorlocs[0]
-            tmin = np.ceil((vmin - t0) / minorstep) * minorstep
-            tmax = np.floor((vmax - t0) / minorstep) * minorstep
+            tmin = ((vmin - t0) // minorstep + 1) * minorstep
+            tmax = ((vmax - t0) // minorstep + 1) * minorstep
             locs = np.arange(tmin, tmax, minorstep) + t0
             cond = np.abs((locs - t0) % majorstep) > minorstep / 10.0
             locs = locs.compress(cond)