From 11bbb3333706acd70a2f2d5bede57d0477d1b699 Mon Sep 17 00:00:00 2001
From: Joakim Hove <joakim.hove@gmail.com>
Date: Mon, 30 Nov 2020 10:14:20 +0100
Subject: [PATCH] Shift the report step argument used when calling UDQ eval

---
 ebos/eclwriter.hh | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/ebos/eclwriter.hh b/ebos/eclwriter.hh
index 05c9a0f1b..1401e234b 100644
--- a/ebos/eclwriter.hh
+++ b/ebos/eclwriter.hh
@@ -328,8 +328,15 @@ public:
                          blockData,
                          aquiferData);
 
-            const auto& udq_config = schedule().getUDQConfig(reportStepNum);
-            udq_config.eval( reportStepNum, schedule().wellMatcher(reportStepNum), summaryState(), udqState() );
+            /*
+              Off-by-one-fun: The reportStepNum argument corresponds to the
+              report step these results will be written to, whereas the argument
+              to UDQ function evaluation corresponds to the report step we are
+              currently on.
+            */
+            auto udq_step = reportStepNum - 1;
+            const auto& udq_config = schedule().getUDQConfig(udq_step);
+            udq_config.eval( udq_step, schedule().wellMatcher(udq_step), summaryState(), udqState() );
 
             buffer = summaryState().serialize();
         }