From 7ed836d12b5f768a960eb475bd6a438c11e076e8 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?L=C3=A9a=20Saviot?= <lea.saviot@numworks.com>
Date: Thu, 14 Jun 2018 14:03:29 +0200
Subject: [PATCH] [apps/reg] Fix non invertible matrix condition

---
 apps/regression/model/model.cpp        | 4 ++--
 poincare/include/poincare/expression.h | 4 +++-
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/apps/regression/model/model.cpp b/apps/regression/model/model.cpp
index d01473e7c..7f06a3667 100644
--- a/apps/regression/model/model.cpp
+++ b/apps/regression/model/model.cpp
@@ -105,8 +105,8 @@ double Model::alphaPrimeCoefficient(Store * store, int series, double * modelCoe
   double result = 0.0;
   if (k == l) {
     result = alphaCoefficient(store, series, modelCoefficients, k, l)*(1.0+lambda);
-    if (result == 0) {
-      result = lambda;
+    if (std::fabs(result) < Expression::epsilon<double>()) {
+      result = 2*Expression::epsilon<double>();
     }
   } else {
     result = alphaCoefficient(store, series, modelCoefficients, l, k);
diff --git a/poincare/include/poincare/expression.h b/poincare/include/poincare/expression.h
index 90cc058fa..cf77d1cf0 100644
--- a/poincare/include/poincare/expression.h
+++ b/poincare/include/poincare/expression.h
@@ -274,6 +274,9 @@ public:
   Coordinate2D nextMaximum(char symbol, double start, double step, double max, Context & context) const;
   double nextRoot(char symbol, double start, double step, double max, Context & context) const;
   Coordinate2D nextIntersection(char symbol, double start, double step, double max, Context & context, const Expression * expression) const;
+
+  /* Evaluation engine */
+  template<typename T> static T epsilon();
 protected:
   /* Constructor */
   Expression() : m_parent(nullptr) {}
@@ -282,7 +285,6 @@ protected:
   /* Evaluation Engine */
   typedef float SinglePrecision;
   typedef double DoublePrecision;
-  template<typename T> static T epsilon();
   constexpr static int k_maxNumberOfSteps = 10000;
 
   /* Simplification */