Description

Illustrates the use of conic formulation for quadratic
programs by implementing rotated quadratic cones.

For the original model in quadratic programming format

   http://www.gams.com/modlib/adddocs/qp1doc.htm

The quadratic component x^T*CoVar(s,t)*x is modeled as:

(|d|-1)*x^T*CoVar(s,t)*x = x^Tdev(s,d)^T*dev(t,d)*x = ||Dx||^2
                         = sum(d, w_i^2) with w = Dx
                        := 2*p*q

which leads to the formulation in this model whose last constraint is
a rotated quadratic cone.

Optional inputs:
  --numdays    investment period in number of days (default: 31).
               Days: 1-100
  --numstocks  number of stocks invested (default: 51)
               Stocks: 1-170

Small Model of Type : QCP

Category : GAMS Model library

Main file : qp7.gms   includes :  qpdata.inc

$title Standard QP Model - conic formulation (QP7,SEQ=271)

$onText
Illustrates the use of conic formulation for quadratic
programs by implementing rotated quadratic cones.

For the original model in quadratic programming format

   http://www.gams.com/modlib/adddocs/qp1doc.htm

The quadratic component x^T*CoVar(s,t)*x is modeled as:

(|d|-1)*x^T*CoVar(s,t)*x = x^Tdev(s,d)^T*dev(t,d)*x = ||Dx||^2
                         = sum(d, w_i^2) with w = Dx
                        := 2*p*q

which leads to the formulation in this model whose last constraint is
a rotated quadratic cone.

Optional inputs:
  --numdays    investment period in number of days (default: 31).
               Days: 1-100
  --numstocks  number of stocks invested (default: 51)
               Stocks: 1-170


Andersen, E, MOSEK Optimization Tools Manual

Kalvelagen, E, Model Building with GAMS. forthcoming

Keywords: quadratic constraint programming, conic optimization, finance
$offText

* Set default number of days and number of stocks
$if not set numdays    $set numdays   31
$if not set numstocks  $set numstocks 51

$include qpdata.inc

Set
   d(days)   'selected days'
   s(stocks) 'selected stocks';

Alias (s,t);

* Select subset of stocks and periods
d(days)   = ord(days) > 1 and ord(days) < %numdays%;
s(stocks) = ord(stocks) < %numstocks%;

Parameter
   mean(stocks)     'mean of daily return'
   dev(stocks,days) 'deviations'
   totmean          'total mean return';

mean(s)  = sum(d, return(s,d))/card(d);
dev(s,d) = return(s,d) - mean(s);
totmean  = sum(s, mean(s))/(card(s));

Variable
   z         'objective variable'
   x(stocks) 'investments'
   w(days)   'intermediate variable for rotated cone'
   p         'intermediate variable for rotated cone'
   q         'intermediate variable for rotated cone';

Positive Variable x, p, q;

Equation
   obj         'objective'
   budget
   retcon      'return constraint'
   wcone(days)
   qone        'conic constraint'
   rcone       'rotated quadratic cone constraint';

obj..       z     =e=  2/(card(d) - 1)*p;

wcone(d)..  w(d)  =e=  sum(s, x(s)*dev(s,d));

* This is really awful:
qone..      q     =e=  1;

* Explicit cone syntax for MOSEK
* rcone..  p + q =c=  sum(d, w(d));

rcone..  2*p*q =g= sum(d, sqr(w(d)));

budget.. sum(s, x(s))         =e= 1.0;

retcon.. sum(s, mean(s)*x(s)) =g= totmean*1.25;

Model qp7 / all /;

solve qp7 using qcp minimizing z;

display x.l;