FIX: Fix regression with mne.viz.plot_evoked (#13481)

Co-authored-by: Daniel McCloy <[email protected]>

Author: mistraube

doc/changes/dev/13481.bugfix.rst

@@ -0,0 +1 @@
+Fix bug with :func:`mne.viz.plot_evoked` when using ``gfp="only"`` or ``gfp=True``, by `Michael Straube`_.

mne/viz/evoked.py

@@ -727,10 +727,12 @@ def _plot_lines(
                 )
                 if gfp_only:
                     y_offset = 0.0
+                    this_ylim = (0, 1.1 * np.max(this_gfp) or 1)
                 else:
                     y_offset = this_ylim[0]
                 this_gfp += y_offset
                 ax.autoscale(False)
+                ax.set_ylim(this_ylim)
                 ax.fill_between(
                     times,
                     y_offset,

tutorials/evoked/30_eeg_erp.py

@@ -286,8 +286,8 @@
     evk.plot(gfp=True, spatial_colors=True, ylim=dict(eeg=[-12, 12]))
 
 # %%
-# To plot the GFP by itself, you can pass ``gfp='only'`` (this makes it easier
-# to read off the GFP data values, because the scale is aligned):
+# To plot the GFP by itself, you can pass ``gfp='only'`` (this makes it easier to
+# read off the GFP data values, because the scale is aligned):
 
 l_aud.plot(gfp="only")