anchor.diff:              | IterationsRemaining -> 
                   // iteration index is an intergral constant
                   ()        
  -
               
           /// derivatives of all ports w.r.t. all variables
           let portDerivs =
  
positive.code:                 dExpr0.Shape.[0]
              | [] -> failwith "output derivatives invalid"
  
          let portType p =
              spec.Channels.[p].Expr.Type
  
          let portSliceShape p =
              spec.Channels.[p].Expr.Shape |> ShapeSpec.withoutAxis spec.Channels.[p].SliceDim
  
          let portSliceElems p =
              p |> portSliceShape |> ShapeSpec.nElem
  
          /// argument of the derivative loop expression
          let args = ResizeArray<ExprT> originalArgs
  
  
negative.code:                 // calculate Jacobians w.r.t. all variables
                  value.Expr |> computeWithRootJacobian incomingJacobian)    
              |> Seq.reduce merge
  
          // go through portContents and create actual port contents
          let ports =
  