ENH: allow extrapolation

jklymak · jklymak · commit 28c659bb13ab · 2018-10-08T17:23:26.000-07:00
diff --git a/lib/matplotlib/colors.py b/lib/matplotlib/colors.py
@@ -1044,9 +1044,14 @@ def __call__(self, value, clip=None):
              raise ValueError("data points must increase monotonically")
         ind = np.where((self._data_points >= vmin) &
                        (self._data_points <= vmax))[0]
+        if clip == None:
+            left, right = -1, 2
+        else:
+            left, right = 0, 1
         result = np.ma.masked_array(np.interp(result,
                                               self._data_points[ind],
-                                              self._norm_points[ind]),
+                                              self._norm_points[ind],
+                                              left=left, right=right),
                                     mask=np.ma.getmask(result))
         if is_scalar:
             result = np.atleast_1d(result)[0]
@@ -1139,12 +1144,11 @@ def __init__(self, vmin=None, vcenter=None, vmax=None):
         # will autoscale to data.
         self.vmin = vmin
         self.vmax = vmax
-        if vcenter is not None and vmax is not None and vcenter > vmax:
-            raise ValueError('vmin, vcenter, and vmax must be in '
-                             'ascending order')
-        if vcenter is not None and vmin is not None and vcenter < vmin:
-            raise ValueError('vmin, vcenter, and vmax must be in '
-                             'ascending order')
+        if vcenter is not None:
+            if ((vmax is not None and vcenter > vmax) or
+                    (vmin is not None and vcenter < vmin)):
+                raise ValueError('DivergingNorm requires that '
+                                 'vmin < vcenter < vmax')
 
         def __call__(value, clip=None):
             """
