Description
This model takes some scenario data (that comes from a true tree), builds a fan and lets ScenRed2 construct a tree. One without loss of information, the other with some reduction requirement. The data is taken from the GAMS/ScenRed2 manual, just the node numbering is different.
Small Model of Type : GAMS
Category : GAMS Model library
Main file : srtree.gms
$title Simple Scenario Tree Construction Example (SRTREE,SEQ=390)
$onText
This model takes some scenario data (that comes from a true tree),
builds a fan and lets ScenRed2 construct a tree. One without loss of
information, the other with some reduction requirement. The data is
taken from the GAMS/ScenRed2 manual, just the node numbering is
different.
H. Heitsch, W. Roemisch, and C. Strugarek
Stability of Multistage Stochastic Programs
SIAM Journal on Optimization 17 (2006), 511-525
Keywords: stochastic programming, scenario tree construction, GAMS ScenRed2
$offText
Set
s 'scenarios' / s1*s4 /
t 'stage' / t1*t5 /
r 'random data' / r1*r4 /;
Parameter p(s) 'probability' / (s1,s2) 0.25, s3 0.3, s4 0.2 /;
Table sdata(s,t,r)
r1 r2 r3 r4
s1.t1 42.5 9.1 7.5 120.0
s1.t2 39.8 11.2 8.4 90.0
s1.t3 37.6 14.0 6.3 110.0
s1.t4 38.9 12.4 8.1 130.0
s1.t5 40.3 14.9 7.2 120.0
s2.t1 42.5 9.1 7.5 120.0
s2.t2 39.8 11.2 8.4 90.0
s2.t3 37.6 14.0 6.3 110.0
s2.t4 38.9 12.4 8.1 130.0
s2.t5 38.4 15.2 8.9 100.0
s3.t1 42.5 9.1 7.5 120.0
s3.t2 39.8 11.2 8.4 90.0
s3.t3 37.6 14.0 6.3 110.0
s3.t4 35.7 13.8 7.5 120.0
s3.t5 37.6 14.9 9.3 80.0
s4.t1 42.5 9.1 7.5 120.0
s4.t2 39.8 11.2 8.4 90.0
s4.t3 37.6 14.0 6.3 110.0
s4.t4 35.7 13.8 7.5 120.0
s4.t5 36.3 12.8 10.3 90.0;
* Construct a fan
$eval nnodes card(s)*(card(t)-1)
Set
n 'nodes' / n0*n%nnodes% /
nn(n) 'next nodes'
anc(n,n) 'ancestor relation';
Parameter
prob(n) 'node probability'
rv(r,n) 'random values';
nn('n0') = yes;
loop(s,
loop(t$(ord(t) < card(t)),
loop(nn(n),
if(sameas('t1',t),
anc(n+1,'n0') = yes;
else
anc(n+1,n) = yes;
);
prob(n+1) = p(s);
rv(r,n+1) = sdata(s,t+1,r);
);
nn(n) = nn(n-1);
);
);
prob('n0') = 1;
rv(r,'n0') = sdata('s1','t1',r);
* Initialize ScenRed2
$set sr2prefix test
$libInclude scenred2
Set anc_noloss(n,n), anc_red(n,n);
Parameter prob_noloss(n), prob_red(n);
* Scenred2 call
ScenredParms('red_percentage') = 0;
$libInclude runscenred2 %sr2prefix% tree_con n anc prob anc_noloss prob_noloss rv
abort$(card(anc_noloss) <> 8) 'scenred tree construction gave incorrect noloss tree', anc_noloss;
display anc_noloss;
* Scenred2 call
ScenredParms('red_num_leaves') = 3;
$libInclude runscenred2 %sr2prefix% tree_con n anc prob anc_red prob_red rv
display anc_red;