public void testDerivativeOfLogarithm()

  {
    var x = RealFunction.parse("∂ln(x)/∂x");
    assertEquals("1/x", x.rootNode.toString());
  } #253

src/main/java/arb/expressions/nodes/unary/FunctionNode.java

@@ -26,6 +26,7 @@
 import arb.expressions.Expression;
 import arb.expressions.FunctionMapping;
 import arb.expressions.Parser;
+import arb.expressions.nodes.LiteralConstantNode;
 import arb.expressions.nodes.Node;
 import arb.expressions.nodes.VariableNode;
 import arb.functions.Function;
@@ -473,6 +474,9 @@ private Node<D, R, F> differentiateBuiltinFunction()
                                 expression).neg(); // derivative of cos is -sin
     case "exp":
       return this; // derivative of exp is exp
+    case "log":
+      return new LiteralConstantNode<>(expression,
+                                       "1").div(arg);
     // Add other built-in function derivatives
     default:
       throw new UnsupportedOperationException("Derivative not implemented for function: " + functionName);

src/test/java/arb/expressions/ExpressionTest.java

@@ -31,6 +31,13 @@
 public class ExpressionTest extends
                             TestCase
 {
+  public void testDerivativeOfLogarithm()
+  {
+    var x = RealFunction.parse("∂ln(x)/∂x");
+    assertEquals("1/x", x.rootNode.toString());
+  }
+
+
   public void testDerivativeOfExponentialFunction()
   {
     var x = RealFunction.parse("∂exp(x)/∂x");