Merge pull request matplotlib#31091 from saakshigupta2002/fix-indexlocator-tick-values-vmax

BUG: Fix IndexLocator.tick_values returning values greater than vmax

Author: timhoffm

lib/matplotlib/tests/test_ticker.py

@@ -604,6 +604,22 @@ def test_set_params(self):
         assert index._base == 7
         assert index.offset == 7
 
+    def test_tick_values_not_exceeding_vmax(self):
+        """
+        Test that tick_values does not return values greater than vmax.
+        """
+        # Test case where offset=0 could cause vmax to be included incorrectly
+        index = mticker.IndexLocator(base=1, offset=0)
+        assert_array_equal(index.tick_values(0, 4), [0, 1, 2, 3, 4])
+
+        # Test case with fractional offset
+        index = mticker.IndexLocator(base=1, offset=0.5)
+        assert_array_equal(index.tick_values(0, 4), [0.5, 1.5, 2.5, 3.5])
+
+        # Test case with base > 1
+        index = mticker.IndexLocator(base=2, offset=0)
+        assert_array_equal(index.tick_values(0, 5), [0, 2, 4])
+
 
 class TestSymmetricalLogLocator:
     def test_set_params(self):

lib/matplotlib/ticker.py

@@ -1767,8 +1767,11 @@ def __call__(self):
         return self.tick_values(dmin, dmax)
 
     def tick_values(self, vmin, vmax):
-        return self.raise_if_exceeds(
-            np.arange(vmin + self.offset, vmax + 1, self._base))
+        # We want tick values in the closed interval [vmin, vmax].
+        # Since np.arange(start, stop) returns values in the semi-open interval
+        # [start, stop), we add a minimal offset so that stop = vmax + eps
+        tick_values = np.arange(vmin + self.offset, vmax + 1e-12, self._base)
+        return self.raise_if_exceeds(tick_values)
 
 
 class FixedLocator(Locator):