From f4a580884b5ae022211b75813e5e3c0cb33aafad Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=89milie=20Feral?= <emilie.feral@numworks.com>
Date: Tue, 10 Jan 2017 12:15:08 +0100
Subject: [PATCH] [apps/graph] Use the poincare derivative calculation to
 compute function derivative

Change-Id: I2b4d9b443935ad789e898e253a22f9d2ab652b6a
---
 apps/constant.cpp                       |  1 -
 apps/constant.h                         |  1 -
 apps/graph/function.cpp                 | 10 +++++-----
 apps/graph/graph/graph_controller.cpp   |  2 +-
 apps/graph/values/values_controller.cpp |  2 +-
 5 files changed, 7 insertions(+), 9 deletions(-)

diff --git a/apps/constant.cpp b/apps/constant.cpp
index f19bfd1f4..8f6c523d4 100644
--- a/apps/constant.cpp
+++ b/apps/constant.cpp
@@ -2,6 +2,5 @@
 
 constexpr int Constant::FloatBufferSizeInScientificMode;
 constexpr int Constant::NumberOfDigitsInMantissaInScientificMode;
-constexpr int Constant::NumberOfDigitsInMantissaForDerivativeNumberInScientificMode;
 constexpr int Constant::FloatBufferSizeInDecimalMode;
 constexpr int Constant::NumberOfDigitsInMantissaInDecimalMode;
diff --git a/apps/constant.h b/apps/constant.h
index 0a4ecd15b..3e2095792 100644
--- a/apps/constant.h
+++ b/apps/constant.h
@@ -5,7 +5,6 @@ class Constant {
 public:
   constexpr static int FloatBufferSizeInScientificMode = 14;
   constexpr static int NumberOfDigitsInMantissaInScientificMode = 7;
-  constexpr static int NumberOfDigitsInMantissaForDerivativeNumberInScientificMode = 3;
   constexpr static int FloatBufferSizeInDecimalMode = 11;
   constexpr static int NumberOfDigitsInMantissaInDecimalMode = 4;
 };
diff --git a/apps/graph/function.cpp b/apps/graph/function.cpp
index 3ef3aaf8f..b25f5def9 100644
--- a/apps/graph/function.cpp
+++ b/apps/graph/function.cpp
@@ -83,11 +83,11 @@ float Function::evaluateAtAbscissa(float x, Context * context) const {
 }
 
 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;
+  Float abscissa = Float(x);
+  Expression * args[2] = {m_expression, &abscissa};
+  Derivative derivative = Derivative();
+  derivative.setArgument(args, 2, true);
+  return derivative.approximate(*context);
 }
 
 }
diff --git a/apps/graph/graph/graph_controller.cpp b/apps/graph/graph/graph_controller.cpp
index b3f70541f..b9c6dfe2f 100644
--- a/apps/graph/graph/graph_controller.cpp
+++ b/apps/graph/graph/graph_controller.cpp
@@ -111,7 +111,7 @@ void GraphController::reloadBannerView() {
     buffer[1] = '\'';
     App * graphApp = (Graph::App *)app();
     float y = f->approximateDerivative(m_cursor.x(), graphApp->localContext());
-    Float(y).convertFloatToText(buffer+8, Constant::FloatBufferSizeInScientificMode, Constant::NumberOfDigitsInMantissaForDerivativeNumberInScientificMode);
+    Float(y).convertFloatToText(buffer+8, Constant::FloatBufferSizeInScientificMode, Constant::NumberOfDigitsInMantissaInScientificMode);
     m_bannerView.setLegendAtIndex(buffer, 2);
   }
   m_bannerView.layoutSubviews();
diff --git a/apps/graph/values/values_controller.cpp b/apps/graph/values/values_controller.cpp
index 4ae13f643..e4e5ab890 100644
--- a/apps/graph/values/values_controller.cpp
+++ b/apps/graph/values/values_controller.cpp
@@ -161,7 +161,7 @@ void ValuesController::willDisplayCellAtLocation(TableViewCell * cell, int i, in
   float x = m_interval.element(j-1);
   App * graphApp = (Graph::App *)app();
   if (isDerivativeColumn(i)) {
-    Float(function->approximateDerivative(x, graphApp->localContext())).convertFloatToText(buffer, Constant::FloatBufferSizeInScientificMode, Constant::NumberOfDigitsInMantissaForDerivativeNumberInScientificMode);
+    Float(function->approximateDerivative(x, graphApp->localContext())).convertFloatToText(buffer, Constant::FloatBufferSizeInScientificMode, Constant::NumberOfDigitsInMantissaInScientificMode);
   } else {
     Float(function->evaluateAtAbscissa(x, graphApp->localContext())).convertFloatToText(buffer, Constant::FloatBufferSizeInScientificMode, Constant::NumberOfDigitsInMantissaInScientificMode);
   }