## Altering equation Topic is solved

Problems with modeling
mapo17af

### Altering equation

I want to alter an existing model in GAMS, by changing an equation.
Please see the screenshot attached for the equation that I want to code and for the existing one that I would like to alter.

I tried the following:

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``````ga(t)=((1-psi)*(ga0)+ psi*ga(t-1))*(exp(-dela*5*((t.val-1)))));
al("1") = a0; loop(t, al(t+1)=al(t)/((1-ga(t))););``````
Hereby, the part

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``(exp(-dela*5*((t.val-1))))``
and

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`` al("1") = a0; loop(t, al(t+1)=al(t)/((1-ga(t))););``
were already in the original code.

My questions are:
- would the above coding give me the preferred equation ? (if I define the parameters earlier onward in the code)
- How should I include epsilon in the formula that I want to code?
Epsilon is an i.i.d. residual from an AR(1) (auto-regressive process of order 1) based on almost 200 years of empirical data. i.e. it is not a parameter that I define myself.

If it is of any relevance: these equations relate to the DICE model of William Nordhaus

Many thanks!
Attachments Preferred equation
Wanted equation.PNG (3.77 KiB) Viewed 622 times Current Equations
OldEquations.PNG (5.71 KiB) Viewed 622 times