diff --git a/poly_matrix/poly_matrix.py b/poly_matrix/poly_matrix.py
index fee55a2..e17bfa3 100644
--- a/poly_matrix/poly_matrix.py
+++ b/poly_matrix/poly_matrix.py
@@ -184,6 +184,18 @@ def __getitem__(self, key):
     def get_size(self):
         return max(self.last_var_i_index, self.last_var_j_index)
 
+    def rename(self, from_labels, to_label):
+        """Rename all keys in from_labels to to_label, summing up the respective values."""
+        for from_label in from_labels:
+            key_j_list = list(self.matrix[from_label].keys())
+            for key_j in key_j_list:
+                if key_j in from_labels:
+                    key_j_to = to_label
+                else:
+                    key_j_to = key_j
+                self[to_label, key_j_to] += self[from_label, key_j]
+        self.drop(from_labels)
+
     def add_variable_i(self, key, size):
         self.variable_dict_i[key] = size
         self.last_var_i_index += size
@@ -531,8 +543,8 @@ def get_matrix_sparse(self, variables=None, output_type="coo", verbose=False):
                     rows, cols = np.nonzero(values)
                     i_list = np.append(i_list, rows + indices_i[key_i])
                     j_list = np.append(j_list, cols + indices_j[key_j])
-                    data_list = np.append(data_list, values[rows,cols])
-                    
+                    data_list = np.append(data_list, values[rows, cols])
+
         if verbose:
             print(f"Filling took {time.time() - t1:.2}s.")
 
@@ -636,6 +648,7 @@ def _plot_matrix(
         variables_i=None,
         variables_j=None,
         reduced_ticks=False,
+        log=False,
         **kwargs,
     ):
         if type(variables_i) is dict:
@@ -663,10 +676,15 @@ def _plot_matrix(
             raise ValueError("untreated case!")
 
         mat = self.get_matrix(variables=(variables_i, variables_j))
+
         if plot_type == "sparse":
             im = ax.spy(mat, **kwargs)
         elif plot_type == "dense":
-            im = ax.matshow(mat.toarray(), **kwargs)
+            if log:
+                mat_plot = np.log10(np.abs(mat.toarray()))
+            else:
+                mat_plot = mat.toarray()
+            im = ax.matshow(mat_plot, **kwargs)
         else:
             raise ValueError(plot_type)
 
@@ -708,6 +726,7 @@ def matshow(
         variables_i=None,
         variables_j=None,
         ax=None,
+        log=False,
         **kwargs,
     ):
         if ax is None:
@@ -720,6 +739,7 @@ def matshow(
             variables=variables,
             variables_i=variables_i,
             variables_j=variables_j,
+            log=log,
             **kwargs,
         )
         return fig, ax, im