We have a model where a block looks something like this

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`y=f(y,x)+y_a`

x=g(y,x)+x_a

Ideally, we would like to link the add-factor in the second equation with the first equation, i.e.

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`d(y_a)=d(x_a).`

to provide some intuition, let y be market prices and x be basic prices. it would be convenient if a change to basic prices from using an add-factor is automatically also applied to market prices. however, endogenizing an add-factor is not allowed in the model object, if I have understood it correctly. I tried to make another model:

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`y=f(y,x)+y_b+y_a`

x=g(y,x)+x_a

d(y_b)=d(x_a) ,

but this specification was not allowed either. I do not want to make the model (Model C):

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`y=f(y,x)+y_b+y_a`

x=g(y,x)+x_b+x_a

d(y_b)=d(x_b)

since, I suspect that the users of our model will forget to use the auxiliary add-factor x_b instead of x_a when adjusting the add-factor. Any change to x from using x_a will thus not also impact y_a.

Is there some way to link the add-factor in one equation to another variable in another equation in the model? One way that could work with a model looking like Model C would be if the SETBOUNDS command could be used on exogenous variables. That way, the user could be warned if she tried to change the add-factor x_a instead of the auxiliary exogenous variable x_b. Can you add the possibility of creating warnings also for exogenous variables? Or is there another smart way of dealing with this issue?

Thomas