added suggested protection against changes to vmin

jpmattern · jpmattern · commit 80019a8aff15 · 2020-10-02T07:41:53.000-07:00
diff --git a/lib/matplotlib/colors.py b/lib/matplotlib/colors.py
@@ -1287,7 +1287,7 @@ def __init__(self, vcenter=0, vmax=None, clip=False):
             >>> norm = mcolors.SymNorm(vmax=4.0)
             >>> data = [-2., 0., 4.]
             >>> norm(data)
-            array([[0.25, 0.5 , 1.  ])
+            array([0.25, 0.5 , 1.  ])
         """
 
         self._vcenter = vcenter
@@ -1329,6 +1329,12 @@ def vcenter(self, vcenter):
                                             self.vmax-self._vcenter)
             self.vmin = 2*self._vcenter - self.vmax
 
+    def __call__(self, value, clip=None):
+        if self.vmax is not None:
+            # enforce symmetry, undo changes to vmin
+            self.vmin = 2*self._vcenter - self.vmax
+        return super().__call__(value, clip=clip)
+
 
 def _make_norm_from_scale(scale_cls, base_norm_cls=None, *, init=None):
     """
