avoid-unnecessary-warning-in-_pcolorargs-function

Within the `_interp_grid function`, unnecessary warnings may be triggered when expanding the grid coordinates. As long as the X coordinates and Y coordinates remain monotonic in their respective directions, negative area grids can be avoided. Therefore, the `require_monotonicity` keyword has been added to avoid triggering monotonicity warnings indiscriminately when calling the function.

Author: wuyao1997

lib/matplotlib/axes/_axes.py

@@ -6027,8 +6027,11 @@ def _pcolorargs(self, funcname, *args, shading='auto', **kwargs):
                 # grid is specified at the center, so define corners
                 # at the midpoints between the grid centers and then use the
                 # flat algorithm.
-                def _interp_grid(X):
-                    # helper for below
+                def _interp_grid(X, require_monotonicity=False):
+                    # helper for below. To ensure the cell edges are calculated 
+                    # correctly, when expanding columns, the monotonicity of 
+                    # X coords needs to be checked. When expanding rows, the 
+                    # monotonicity of Y coords needs to be checked.
                     if np.shape(X)[1] > 1:
                         dX = np.diff(X, axis=1) * 0.5
                         if not (np.all(dX >= 0) or np.all(dX <= 0)):
@@ -6051,11 +6054,11 @@ def _interp_grid(X):
                     return X
 
                 if ncols == Nx:
-                    X = _interp_grid(X)
+                    X = _interp_grid(X, require_monotonicity=True)
                     Y = _interp_grid(Y)
                 if nrows == Ny:
                     X = _interp_grid(X.T).T
-                    Y = _interp_grid(Y.T).T
+                    Y = _interp_grid(Y.T, require_monotonicity=True).T
                 shading = 'flat'
 
         C = cbook.safe_masked_invalid(C, copy=True)