From be247b0392602fea584b0af5c3d03f6a59fa4089 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=89milie=20Feral?= <emilie.feral@numworks.com>
Date: Wed, 4 Jan 2017 17:29:06 +0100
Subject: [PATCH] [apps/graph] When computing derivative function at abscissa,
 round the result

Change-Id: I23817dda6ff9fe335e819086ecad5119eba1d948
---
 apps/graph/function.cpp | 2 ++
 apps/graph/function.h   | 1 +
 2 files changed, 3 insertions(+)

diff --git a/apps/graph/function.cpp b/apps/graph/function.cpp
index a69a0beda..3ef3aaf8f 100644
--- a/apps/graph/function.cpp
+++ b/apps/graph/function.cpp
@@ -1,5 +1,6 @@
 #include "function.h"
 #include <string.h>
+#include <math.h>
 
 namespace Graph {
 
@@ -85,6 +86,7 @@ float Function::approximateDerivative(float x, Context * context) const {
   float functionPlus = evaluateAtAbscissa(x + k_epsilon, context);
   float functionMinus = evaluateAtAbscissa(x - k_epsilon, context);
   float growthRate = (functionPlus - functionMinus)/(2*k_epsilon);
+  growthRate = roundf(growthRate/k_precision)*k_precision;
   return growthRate;
 }
 
diff --git a/apps/graph/function.h b/apps/graph/function.h
index d55778d2d..26884032e 100644
--- a/apps/graph/function.h
+++ b/apps/graph/function.h
@@ -27,6 +27,7 @@ public:
   float approximateDerivative(float x, Context * context) const;
 private:
   constexpr static float k_epsilon = 0.0001f;
+  constexpr static float k_precision = 0.01f;
   constexpr static int k_bodyLength = 255;
   char m_text[k_bodyLength];
   const char * m_name;