From b78a989e71fabc0ed9022e9a387c55dd7aaf2de6 Mon Sep 17 00:00:00 2001
From: Sevy Harris <30695172+sevyharris@users.noreply.github.com>
Date: Thu, 22 Jan 2026 16:04:13 -0500
Subject: [PATCH] add warning not to initialize walkers in same starting place

Add validation for walker initial positions.
---
 zeus/ensemble.py | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/zeus/ensemble.py b/zeus/ensemble.py
index 4242d87..368986a 100644
--- a/zeus/ensemble.py
+++ b/zeus/ensemble.py
@@ -494,6 +494,9 @@ def sample(self,
         if not np.all(np.isfinite(Z)):
             raise ValueError('Invalid walker initial positions! \n' +
                              'Initialise walkers from positions of finite log probability.')
+        if self.nwalkers > 1 and (X == X[0]).all():
+            raise ValueError('Invalid walker initial positions! \n' +
+                             'Initialise walkers from different starting positions.')
         batch = list(np.arange(self.nwalkers))
 
         # Extend saving space
@@ -724,4 +727,4 @@ def sample(self,
 class sampler(EnsembleSampler):
     def __init__(self, *args, **kwargs):
         logging.warning('The sampler class has been deprecated. Please use the new EnsembleSampler class.')
-        super().__init__(*args, **kwargs)
\ No newline at end of file
+        super().__init__(*args, **kwargs)