[NB] make correct div operators when differentiating (#13626)

Author: kabdelhak

OMCompiler/Compiler/NBackEnd/Util/NBDifferentiate.mo

@@ -1765,7 +1765,8 @@ public
           (_, sizeClass) := Operator.classify(operator);
           addOp := Operator.fromClassification((NFOperator.MathClassification.ADDITION, sizeClass), operator.ty);
           mulOp := Operator.fromClassification((NFOperator.MathClassification.MULTIPLICATION, sizeClass), operator.ty);
-          powOp := Operator.fromClassification((NFOperator.MathClassification.POWER, sizeClass), operator.ty);
+          powOp := Operator.fromClassification((NFOperator.MathClassification.POWER,
+            Operator.combineSizeClassification(sizeClass, NFOperator.SizeClassification.SCALAR)), operator.ty);
       then (Expression.MULTARY(
               {Expression.MULTARY(
                 {Expression.BINARY(exp1, mulOp, diffExp2)},              // fg'
@@ -1894,7 +1895,8 @@ public
           // create addition and power operator
           (_, sizeClass) := Operator.classify(operator);
           addOp := Operator.fromClassification((NFOperator.MathClassification.ADDITION, sizeClass), operator.ty);
-          powOp := Operator.fromClassification((NFOperator.MathClassification.POWER, sizeClass), operator.ty);
+          powOp := Operator.fromClassification((NFOperator.MathClassification.POWER,
+            Operator.combineSizeClassification(sizeClass, NFOperator.SizeClassification.SCALAR)), operator.ty);
           // f'
           (diff_arguments, diffArguments) := differentiateMultaryMultiplicationArgs(arguments, diffArguments, operator);
           diff_enumerator := Expression.MULTARY(diff_arguments, {}, addOp);

OMCompiler/Compiler/NFFrontEnd/NFOperator.mo

@@ -853,6 +853,19 @@ public
     (_, scl) := classify(op);
   end getSizeClassification;
 
+  function combineSizeClassification
+    input SizeClassification scl1;
+    input SizeClassification scl2;
+    output SizeClassification scl;
+  algorithm
+    scl := match (scl1, scl2)
+      // Todo: more cases?
+      case (SizeClassification.ELEMENT_WISE, SizeClassification.SCALAR) then SizeClassification.ARRAY_SCALAR;
+      case (SizeClassification.SCALAR, SizeClassification.ELEMENT_WISE) then SizeClassification.SCALAR_ARRAY;
+      else scl1;
+    end match;
+  end combineSizeClassification;
+
   function isDashClassification
     input MathClassification mcl;
     output Boolean b;