This lesson is divided into two parts : the information needed to model risk and how to write in GAMS. Watch the first video and try to write the model in question ON YOUR OWN before you watch the second one.
| 1) Video 1 : Theory |
 (15 min)
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| 2) Example : Income variability |
- open GAMS
- open the model primal0_risk_base.gms
- Add the equations of random income calculation and check the random income values in the output file
| State of nature |
Probability |
Gross margin of wheat |
Gross margin of maize |
| E1 |
0.2 |
460 |
2000 |
| E2 |
0.2 |
440 |
500 |
| E3 |
0.2 |
450 |
300 |
| E4 |
0.2 |
430 |
1400 |
| E5 |
0.2 |
470 |
800 |
| AVERAGE |
|
450 |
1000 |
The model is therefore written as follows :
Max Z = 450×1+1000×2
avec x1+x2 ≤ 50
25×1+50×2 ≤ 2000
460×1+2000×2 = RAL1
440×1+500×2 = RAL2
450×1+300×2 = RAL3
430×1+1400×2 = RAL4
470×1+800×2 = RAL5 x1,x2 ≥ 0
Add 5 calculation constraints such as :
equations
revenuAlea1;
revenuAlea1.. RAL1=e=sum(C, MB(‘E1’,C)*X(C)] ;
Or ass a constraint that is dependent on set E (like in lesson 12 concerning periods)
equations
revenuAlea(E);
revenuAlea(E).. RAL(E)=e=sum(C, MB(E,C)*X(C)];
It is now your turn to write in GAMS ! |
| 3) Correction-lesson |
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