From b1003321fc7bacce318b01159eee6f7319c3a1c1 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E8=97=A4=E6=9C=A8=E6=BD=A4=E4=B8=80?=
 <fujikijunichi@MacBook-Pro.local>
Date: Thu, 24 Sep 2026 06:49:04 +0900
Subject: [PATCH 1/2] Use stable logsumexp in grid plots

---
 cosmosis/plotting/grid_plots.py  | 11 ++++++++---
 cosmosis/test/test_grid_plots.py | 16 ++++++++++++++++
 2 files changed, 24 insertions(+), 3 deletions(-)
 create mode 100644 cosmosis/test/test_grid_plots.py

diff --git a/cosmosis/plotting/grid_plots.py b/cosmosis/plotting/grid_plots.py
index 3877b1e6..c50994fa 100644
--- a/cosmosis/plotting/grid_plots.py
+++ b/cosmosis/plotting/grid_plots.py
@@ -23,6 +23,7 @@
 from .plotter import Plotter
 import itertools
 import scipy.optimize
+from scipy.special import logsumexp
 try:
 	from cosmosis import output as output_module
 except ImportError:
@@ -30,6 +31,11 @@
 
 
 class GridPlotter(Plotter):
+	@staticmethod
+	def _logsumexp(values):
+		"""Stable log(sum(exp(values))) for grid marginalization."""
+		return logsumexp(values)
+
 	#def __init__(self, *args, **kwargs):
 		# super(GridPlotter, self).__init__(*args, **kwargs)
 		# convert the loaded chain data sets into grids
@@ -69,7 +75,7 @@ def _plot_1d(self, name1):
 		#marginalize
 		for k,v1 in enumerate(vals1):
 			w = np.where(cols1==v1)
-			like_sum[k] = np.log(np.exp(like[w]).sum())
+			like_sum[k] = self._logsumexp(like[w])
 		like = like_sum.flatten()
 
 		#linearly interpolate
@@ -149,7 +155,7 @@ def _plot_2d(self, name1, name2, log_like=True):
 		for k,(v1, v2) in enumerate(itertools.product(vals1, vals2)):
 			w = np.where((cols1==v1)&(cols2==v2))
 			i,j = np.unravel_index(k, like_sum.shape)
-			like_sum[i,j] = np.log(np.exp(like[w]).sum())
+			like_sum[i,j] = self._logsumexp(like[w])
 		like = like_sum.flatten()
 
 		#Normalize the log-likelihood to peak=0
@@ -210,4 +216,3 @@ def toggle_edge(edges, x1,y1,x2,y2):
 		sm = pylab.cm.ScalarMappable(cmap=colormap, norm=norm)
 		sm._A = [] #hack from StackOverflow to make this work
 		pylab.colorbar(sm, label='Likelihood')
-
diff --git a/cosmosis/test/test_grid_plots.py b/cosmosis/test/test_grid_plots.py
new file mode 100644
index 00000000..e70552a1
--- /dev/null
+++ b/cosmosis/test/test_grid_plots.py
@@ -0,0 +1,16 @@
+import numpy as np
+
+from cosmosis.plotting.grid_plots import GridPlotter
+
+
+def test_grid_logsumexp_handles_extreme_log_likelihoods():
+    values = np.array([1000.0, 999.0, -1000.0])
+    result = GridPlotter._logsumexp(values)
+    expected = 1000.0 + np.log1p(np.exp(-1.0))
+    np.testing.assert_allclose(result, expected)
+    assert np.isfinite(result)
+
+
+def test_grid_logsumexp_empty_group_is_negative_infinity():
+    result = GridPlotter._logsumexp(np.array([]))
+    assert result == -np.inf

From c10ef96299fe067e846a221db410bcee9ab52cfb Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E8=97=A4=E6=9C=A8=E6=BD=A4=E4=B8=80?=
 <fujikijunichi@MacBook-Pro.local>
Date: Thu, 24 Sep 2026 07:33:59 +0900
Subject: [PATCH 2/2] Handle empty grid marginalization groups

---
 cosmosis/plotting/grid_plots.py | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/cosmosis/plotting/grid_plots.py b/cosmosis/plotting/grid_plots.py
index c50994fa..3a2a39ef 100644
--- a/cosmosis/plotting/grid_plots.py
+++ b/cosmosis/plotting/grid_plots.py
@@ -34,6 +34,8 @@ class GridPlotter(Plotter):
 	@staticmethod
 	def _logsumexp(values):
 		"""Stable log(sum(exp(values))) for grid marginalization."""
+		if np.size(values) == 0:
+			return -np.inf
 		return logsumexp(values)
 
 	#def __init__(self, *args, **kwargs):