Added check for when material list is less than fractal bins/materials

gprMax/cmds_geometry/fractal_box.py

@@ -21,6 +21,7 @@ import logging
 import numpy as np
 
 from ..fractals import FractalVolume
+from ..materials import ListMaterial
 from .cmds_geometry import UserObjectGeometry, rotate_2point_object
 
 logger = logging.getLogger(__name__)
@@ -139,6 +140,12 @@ class FractalBox(UserObjectGeometry):
                 logger.exception(f'{self.__str__()} must be used with more than ' +
                                  'one material from the mixing model.')
                 raise ValueError
+            if isinstance(mixingmodel, ListMaterial):
+                if nbins > len(mixingmodel.mat):
+                    logger.exception(f'{self.__str__()} too many materials/bins ' +
+                                        'requested compared to materials in ' +
+                                        'mixing model.')
+                    raise ValueError
             # Create materials from mixing model as number of bins now known 
             # from fractal_box command.
             mixingmodel.calculate_properties(nbins, grid)