[poincare/cosine] Implemented didDerivate and unaryFunctionDifferential for Cosine

Derivation now propagates as expected on cosines.

Change-Id: I6f5af48ac7462c5b8e77ff1a6428a65bf6c0c7de

poincare/include/poincare/cosine.h

@@ -34,6 +34,10 @@ private:
   LayoutShape leftLayoutShape() const override { return LayoutShape::MoreLetters; };
   LayoutShape rightLayoutShape() const override { return LayoutShape::BoundaryPunctuation; }
 
+  // Derivation
+  bool didDerivate(ReductionContext reductionContext, Expression symbol, Expression symbolValue) override;
+  Expression unaryFunctionDifferential() override;
+
   // Evaluation
   Evaluation<float> approximate(SinglePrecision p, Context * context, Preferences::ComplexFormat complexFormat, Preferences::AngleUnit angleUnit) const override {
     return ApproximationHelper::Map<float>(this, context, complexFormat, angleUnit,computeOnComplex<float>);
@@ -51,6 +55,9 @@ public:
   static constexpr Expression::FunctionHelper s_functionHelper = Expression::FunctionHelper("cos", 1, &UntypedBuilderOneChild<Cosine>);
 
   Expression shallowReduce(ExpressionNode::ReductionContext reductionContext);
+
+  bool didDerivate(ExpressionNode::ReductionContext reductionContext, Expression symbol, Expression symbolValue);
+  Expression unaryFunctionDifferential();
 };
 
 }

poincare/src/cosine.cpp

@@ -1,7 +1,11 @@
 #include <poincare/cosine.h>
 #include <poincare/complex.h>
+#include <poincare/derivative.h>
 #include <poincare/layout_helper.h>
+#include <poincare/multiplication.h>
+#include <poincare/rational.h>
 #include <poincare/serialization_helper.h>
+#include <poincare/sine.h>
 
 #include <cmath>
 
@@ -34,6 +38,14 @@ Expression CosineNode::shallowReduce(ReductionContext reductionContext) {
   return Cosine(this).shallowReduce(reductionContext);
 }
 
+bool CosineNode::didDerivate(ReductionContext reductionContext, Expression symbol, Expression symbolValue) {
+  return Cosine(this).didDerivate(reductionContext, symbol, symbolValue);
+}
+
+Expression CosineNode::unaryFunctionDifferential() {
+  return Cosine(this).unaryFunctionDifferential();
+}
+
 Expression Cosine::shallowReduce(ExpressionNode::ReductionContext reductionContext) {
   {
     Expression e = Expression::defaultShallowReduce();
@@ -45,5 +57,13 @@ Expression Cosine::shallowReduce(ExpressionNode::ReductionContext reductionConte
   return Trigonometry::shallowReduceDirectFunction(*this, reductionContext);
 }
 
+bool Cosine::didDerivate(ExpressionNode::ReductionContext reductionContext, Expression symbol, Expression symbolValue) {
+  Derivative::DerivateUnaryFunction(*this, symbol, symbolValue);
+  return true;
+}
+
+Expression Cosine::unaryFunctionDifferential() {
+  return Multiplication::Builder(Rational::Builder(-1), Sine::Builder(childAtIndex(0).clone()));
+}
 
 }

poincare/test/derivative.cpp

@@ -44,4 +44,6 @@ QUIZ_CASE(poicare_differential_unary_functions) {
   assert_parses_and_reduces_as("diff(sin(x),x,π)","-1");
   assert_parses_and_reduces_as("diff(sin(2y),y,π/12)","√(3)");
   assert_parses_and_reduces_as("diff(sin(2x)+sin(3x),x,π/6)","1");
+
+  assert_parses_and_reduces_as("diff(cos(x),x,π/2)","-1");
 }