From 642eeb973323ba412b368218aa9a7f4012ef0700 Mon Sep 17 00:00:00 2001
From: mtfishman <mfishman@flatironinstitute.org>
Date: Mon, 24 Nov 2025 17:36:53 -0500
Subject: [PATCH] Access truncation errors in apply

---
 Project.toml       | 2 +-
 src/abstractmps.jl | 4 +++-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/Project.toml b/Project.toml
index 54859de..753334b 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,7 +1,7 @@
 name = "ITensorMPS"
 uuid = "0d1a4710-d33b-49a5-8f18-73bdf49b47e2"
 authors = ["Matthew Fishman <mfishman@flatironinstitute.org>", "Miles Stoudenmire <mstoudenmire@flatironinstitute.org>"]
-version = "0.3.25"
+version = "0.3.26"
 
 [deps]
 Adapt = "79e6a3ab-5dfb-504d-930d-738a2a938a0e"
diff --git a/src/abstractmps.jl b/src/abstractmps.jl
index 73905d6..c1fbd1d 100644
--- a/src/abstractmps.jl
+++ b/src/abstractmps.jl
@@ -1968,6 +1968,7 @@ function (::Type{MPST})(
         leftinds = nothing,
         orthocenter::Integer = length(sites),
         tags = [defaultlinktags(i) for i in 1:(length(sites) - 1)],
+        post_factorize_callback = Returns(nothing),
         kwargs...,
     ) where {MPST <: AbstractMPS}
     N = length(sites)
@@ -1989,7 +1990,8 @@ function (::Type{MPST})(
         if !isnothing(l)
             Lis = unioninds(Lis, l)
         end
-        L, R = factorize(Ã, Lis; kwargs..., tags = tags[n], ortho = "left")
+        L, R, spec = factorize(Ã, Lis; kwargs..., tags = tags[n], ortho = "left")
+        post_factorize_callback(; truncation_error = spec.truncerr)
         l = commonind(L, R)
         ψ[n] = L
         Ã = R