Type VariableRef has no field head

Specific Domains
1

Hi All,

I try to formulate an objective function, like x*log(x), x is a nonlinear expression. However, when I run the optimization, it shows type VariableRef has no field head. Anyone else saw this message?

JuMP.@NLexpression(model, R1, (ami*tstp)/dc )
JuMP.@NLexpression(model, R2, log((ami * tstp)/dc) )
JuMP.@NLexpression(model, R, R1 * R2 )

return JuMP.@NLobjective(model, Min,

     R
  )

The ami, tstp, and dc are very long nonlinear equations. If needed, I can post as well.

When I try to solve the optimization, it shows

type VariableRef has no field head

I also test the expression of R1 and R2 for the objective function individually and they work fine. However, when I use the expression of R1*R2 / R, it shows the error.

Thanks