From f8bcec2b4bdf2c45c28829a63aa1d509a38d238d Mon Sep 17 00:00:00 2001
From: Jonathan Taylor <jonathan.taylor@stanford.edu>
Date: Thu, 17 Apr 2025 16:09:33 -0700
Subject: [PATCH] fix indexing / sorting for initializing gradient with no warm
 start

---
 adelie/solver.py | 26 +++++++++++++++-----------
 1 file changed, 15 insertions(+), 11 deletions(-)

diff --git a/adelie/solver.py b/adelie/solver.py
index b82dc735..08343708 100644
--- a/adelie/solver.py
+++ b/adelie/solver.py
@@ -284,16 +284,20 @@ def gaussian_cov(
         active_set[:active_set_size] = np.arange(active_set_size)
         rsq = 0
 
-        subset = np.array([
-            np.arange(groups[ss], groups[ss] + group_sizes[ss]) 
-            for ss in screen_set
-        ])
-        order = np.argsort(subset)
-        indices = subset[order]
-        values = screen_beta[order]
-
-        grad = np.empty(p, dtype=dtype)
-        A.mul(indices, values, grad)
+        if screen_set.size > 0:
+            subset = np.hstack([
+                np.arange(groups[ss], groups[ss] + group_sizes[ss]) 
+                for ss in screen_set])
+            order = np.argsort(subset)
+            indices = subset[order]
+            values = screen_beta[order]
+
+            grad = np.empty(p, dtype=dtype)
+            A.mul(indices, values, grad)
+        else:
+            # it actually just feels like this is what we might as well set as grad...
+            grad = np.zeros(p, dtype=dtype)
+            
         grad = v - grad
 
     else:
@@ -1425,4 +1429,4 @@ def css_cov(
         n_threads=n_threads
     )
 
-    return state.solve()
\ No newline at end of file
+    return state.solve()