qr_stabilized: fix rare bug for complex tensors

jcmgray · Jan 24, 2024 · 9b11068 · 9b11068
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diff --git a/docs/changelog.md b/docs/changelog.md
@@ -2,6 +2,17 @@
 
 Release notes for `quimb`.
 
+(whats-new-1-7-1)=
+## v1.7.1 (unreleased)
+
+**Bug fixes:**
+
+- fix bug in [`kruas_op`](quimb.kraus_op) when operator spanned multiple
+  subsystems ({issue}`214`)
+- fix bug in [`qr_stabilized`](quimb.decomp.qr_stabilized) when the diagonal of
+  `R` has significant imaginary parts.
+
+
 (whats-new-1-7-0)=
 ## v1.7.0 (12-08-2023)
 

diff --git a/quimb/tensor/decomp.py b/quimb/tensor/decomp.py
@@ -616,7 +616,7 @@ def qr_stabilized(x, backend=None):
         # stabilize the diagonal of R
         rd = do("diag", R)
         s = sgn(rd)
-        Q = rdmul(Q, s)
+        Q = rdmul(Q, do("conj", s))
         R = ldmul(s, R)
         return Q, None, R
 
@@ -629,7 +629,7 @@ def qr_stabilized_numba(x):
         rii = R[i, i]
         si = sgn_numba(rii)
         if si != 1.0:
-            Q[:, i] *= si
+            Q[:, i] *= np.conj(si)
             R[i, i:] *= si
     return Q, None, R