[FIX] Fix overlapping titles for plot_matrix function (#3899)

* Simplify add title

* [full doc] build examples

* Update test

nilearn/plotting/matrix_plotting.py

@@ -325,18 +325,9 @@ def plot_matrix(
         fig.tight_layout()
 
     if title is not None:
-        # Adjust the size
-        text_len = np.max([len(t) for t in title.split("\n")])
-        size = axes.bbox.size[0] / text_len
-        axes.text(
-            0.95,
-            0.95,
-            title,
-            horizontalalignment="right",
-            verticalalignment="top",
-            transform=axes.transAxes,
-            size=size,
-        )
+        axes.set_title(title, size=16)
+        fig.tight_layout()
+
     return display
 
 

nilearn/plotting/tests/test_matrix_plotting.py

@@ -156,10 +156,10 @@ def test_matrix_plotting_labels(mat, lab):
 @pytest.mark.parametrize("title", ["foo", "foo bar", " ", None])
 def test_matrix_plotting_set_title(mat, labels, title):
     ax = plot_matrix(mat, labels=labels, title=title)
-    nb_txt = 0 if title is None else 1
-    assert len(ax._axes.texts) == nb_txt
+    nb_txt = 0 if title is None else len(title)
+    assert len(ax._axes.title.get_text()) == nb_txt
     if title is not None:
-        assert ax._axes.texts[0].get_text() == title
+        assert ax._axes.title.get_text() == title
     plt.close()