Fix PCP visualization not displaying plots #752

- Use plt.plot() instead of pymoo.visualization.util.plot() in PCP
  The util.plot() function expects 2D Pareto front arrays, not (x, y) line data
- Remove forced Agg backend from matplotlib.py to allow interactive displays
- Make backend check case-insensitive in plot.py (Agg vs agg)

Author: blankjul

pymoo/core/plot.py

@@ -170,7 +170,7 @@ def show(self, **kwargs):
         self.plot_if_not_done_yet()
 
         # in a notebook the plot method need not to be called explicitly
-        if not in_notebook() and matplotlib.get_backend() != "agg":
+        if not in_notebook() and matplotlib.get_backend().lower() != "agg":
             plt.show(**kwargs)
             plt.close()
 

pymoo/visualization/matplotlib.py

@@ -15,10 +15,7 @@
     from matplotlib import animation
     from matplotlib.collections import LineCollection, PatchCollection
     from matplotlib.colors import ListedColormap
-    
-    # Set backend and configuration
-    matplotlib.use('Agg', force=False)  # Use non-interactive backend by default
-    
+
     _MATPLOTLIB_AVAILABLE = True
 
     # Export all commonly used matplotlib objects

pymoo/visualization/pcp.py

@@ -1,10 +1,10 @@
 import numpy as np
 
-import pymoo.visualization.util
 from pymoo.docs import parse_doc_string
 from pymoo.core.plot import Plot
 from pymoo.util.misc import set_if_none, set_if_none_from_tuples
 from pymoo.visualization.util import parse_bounds, normalize
+from pymoo.visualization.matplotlib import plt
 
 
 class PCP(Plot):
@@ -79,7 +79,7 @@ def _do(self):
             set_if_none(_kwargs, "color", self.colors[k % len(self.colors)])
 
             for i in range(len(F)):
-                pymoo.visualization.util.plot(np.arange(F.shape[1]), F[i, :], **_kwargs)
+                plt.plot(np.arange(F.shape[1]), F[i, :], **_kwargs)
 
         # Plot the parallel coordinate axes
         for i in range(self.n_dim):