From 05098b09c3bb2c3c001a9722f9b63d88df2c9430 Mon Sep 17 00:00:00 2001
From: Tom Veasey <tveasey@users.noreply.github.com>
Date: Fri, 17 Jul 2020 08:47:42 +0100
Subject: [PATCH] [ML] Testing for no change should not use the change trend
 model

Change #1391 introduced a subtle error: when computing the likelihood of no change
we should use a reference to the current time series trend model, not the copy of the
model which assumes a change is occurring.
---
 lib/maths/CTimeSeriesChangeDetector.cc | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/lib/maths/CTimeSeriesChangeDetector.cc b/lib/maths/CTimeSeriesChangeDetector.cc
index 797865af5b..49cc0862a5 100644
--- a/lib/maths/CTimeSeriesChangeDetector.cc
+++ b/lib/maths/CTimeSeriesChangeDetector.cc
@@ -98,13 +98,13 @@ CUnivariateTimeSeriesChangeDetector::CUnivariateTimeSeriesChangeDetector(
     : m_MinimumTimeToDetect{minimumTimeToDetect}, m_MaximumTimeToDetect{maximumTimeToDetect},
       m_MinimumDeltaBicToDetect{minimumDeltaBicToDetect}, m_SampleCount{0},
       m_DecisionFunction{0.0}, m_TrendModel{trendModel->clone()} {
+    m_ChangeModels.push_back(
+        std::make_unique<CUnivariateNoChangeModel>(trendModel, residualModel));
     this->initChangeModels(residualModel);
 }
 
 void CUnivariateTimeSeriesChangeDetector::initChangeModels(TPriorPtr residualModel) {
-    m_ChangeModels.clear();
-    m_ChangeModels.push_back(
-        std::make_unique<CUnivariateNoChangeModel>(m_TrendModel, residualModel));
+    m_ChangeModels.resize(1);
     m_ChangeModels.push_back(
         std::make_unique<CUnivariateLevelShiftModel>(m_TrendModel, residualModel));
     if (m_TrendModel->seasonalComponents().size() > 0) {