From 41524ebe4c975fa0b383cb485ad650879cb4260f Mon Sep 17 00:00:00 2001
From: Stephen Crowley <stephencrowley214@gmail.com>
Date: Wed, 27 Nov 2024 16:29:08 -0600
Subject: [PATCH] https://github.com/crowlogic/arb4j/issues/253 fix derivative
 of exponentiation

---
 src/main/java/arb/expressions/nodes/Node.java | 24 +++++++++++++++++++
 .../nodes/binary/ExponentiationNode.java      |  4 +++-
 2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/src/main/java/arb/expressions/nodes/Node.java b/src/main/java/arb/expressions/nodes/Node.java
index ea286bc15..02bcf0e5a 100644
--- a/src/main/java/arb/expressions/nodes/Node.java
+++ b/src/main/java/arb/expressions/nodes/Node.java
@@ -17,7 +17,10 @@
 import arb.expressions.Compiler;
 import arb.expressions.Expression;
 import arb.expressions.nodes.binary.AdditionNode;
+import arb.expressions.nodes.binary.DivisionNode;
+import arb.expressions.nodes.binary.ExponentiationNode;
 import arb.expressions.nodes.binary.MultiplicationNode;
+import arb.expressions.nodes.binary.SubtractionNode;
 import arb.functions.Function;
 
 /**
@@ -210,6 +213,20 @@ public boolean isPossiblyNegative()
     return false;
   }
 
+  public Node<D, R, F> pow(Node<D, R, F> exponent)
+  {
+    return new ExponentiationNode<>(expression,
+                                    this,
+                                    exponent);
+  }
+
+  public Node<D, R, F> sub(Node<D, R, F> subtrahend)
+  {
+    return new SubtractionNode<>(expression,
+                                 this,
+                                 subtrahend);
+  }
+
   public Node<D, R, F> add(Node<D, R, F> addend)
   {
     return new AdditionNode<>(expression,
@@ -217,6 +234,13 @@ public Node<D, R, F> add(Node<D, R, F> addend)
                               addend);
   }
 
+  public Node<D, R, F> div(Node<D, R, F> divisor)
+  {
+    return new DivisionNode<>(expression,
+                              this,
+                              divisor);
+  }
+
   public Node<D, R, F> mul(Node<D, R, F> multiplicand)
   {
     return new MultiplicationNode<>(expression,
diff --git a/src/main/java/arb/expressions/nodes/binary/ExponentiationNode.java b/src/main/java/arb/expressions/nodes/binary/ExponentiationNode.java
index 86a485ca3..addea57ae 100644
--- a/src/main/java/arb/expressions/nodes/binary/ExponentiationNode.java
+++ b/src/main/java/arb/expressions/nodes/binary/ExponentiationNode.java
@@ -5,6 +5,7 @@
 import arb.documentation.BusinessSourceLicenseVersionOnePointOne;
 import arb.documentation.TheArb4jLibrary;
 import arb.expressions.Expression;
+import arb.expressions.nodes.LiteralConstantNode;
 import arb.expressions.nodes.Node;
 import arb.expressions.nodes.VariableNode;
 import arb.functions.Function;
@@ -65,7 +66,8 @@ public Node<D, R, F> integral(VariableNode<D, R, F> variable)
   @Override
   public Node<D, R, F> differentiate(VariableNode<D, R, F> variable)
   {
-    return this;
+    return right.mul(left.pow(right.sub(new LiteralConstantNode<>(expression,
+                                                                  "1"))));
   }
 
   @Override