one unknown-one equation

GAMS
1

Hello Dear users
I am trying to start a project about phase equilibria so I choose gams as a powerfull tool for optimization and solving nonlinear equation system,
but at first step of testing NLP gams solver, I have a trouble with solving the following code has been written in GAMS to solve one unknown-one equation system:

=======================================================================

  • a hydrocarbon mixture with the following overall composition is flashed in a
  • separator at 50 psia and 100 F
    set i components /c3,ic4,nc4,ic5,nc5,c6/;
    alias (i,j);
    scalar ptotal,T;
    ptotal=50;T=100;
    ===============================================================================
    parameter Z(i) overall composition
    /c3 0.20
    ic4 0.10
    nc4 0.10
    ic5 0.20
    nc5 0.20
    c6 0.20/;
    Z(i)=z(i)/sum(j,z(j));
    parameter psat(i) vapor pressure at T from cox chart
    /c3 190
    ic4 72.2
    nc4 51.6
    ic5 20.44
    nc5 15.57
    c6 4.956/;
    parameter Kvalue(i);
    Kvalue(i)=psat(i)/Ptotal;
    display kvalue;
    ===============================================================================
    variable nv;
    equation E1;
    E1…sum( i, z(i)    (Kvalue(i)-1)/(nv    (Kvalue(i)-1))+1 ) =e=0;
    parameter A,B;
    A=sum(i,z(i)(Kvalue(i)-1));B=sum(i,z(i)(Kvalue(i)-1)/Kvalue(i));
    model flash /All/;
    nv.l=A/(A-B);
    nv.lo=0;
    nv.up=1;
    *option nlp=minos
    SOLVE flash USING nlp MINIMIZING nv;
    =======================================================
    How can I modify above code to solve it??

cheers

–
To unsubscribe from this group and stop receiving emails from it, send an email to gamsworld+unsubscribe@googlegroups.com.
To post to this group, send email to gamsworld@googlegroups.com.
Visit this group at http://groups.google.com/group/gamsworld.
For more options, visit https://groups.google.com/groups/opt_out.

2

Hi Mrtz Manesh



You initialize nv to a value computed from your data and I assume that you think this should be the solution. However, the equation listing shows that the equation is quite infeasible:



---- E1 =E=



E1… - (219.35663064419)*nv =E= -6 ; (LHS = 14.8106931182909, INFES = 20.8106931182909 ****)



I have removed your bounds on nv and the model solves and gives nv = -0.1667



I will guess that you have your parenthesis wrong in equation e1.



Regards



Arne


\

Arne Stolbjerg Drud

ARKI Consulting & Development A/S

Bagsvaerdvej 246A, DK-2880 Bagsvaerd, Denmark

Phone: (+45) 44 49 03 23, Fax: (+45) 44 49 03 33, email: adrud@arki.dk



From: gamsworld@googlegroups.com [mailto:gamsworld@googlegroups.com] On Behalf Of Mrtz manesh
Sent: Thursday, November 21, 2013 12:53 AM
To: gamsworld@googlegroups.com
Subject: one unknown-one equation



Hello Dear users

I am trying to start a project about phase equilibria so I choose gams as a powerfull tool for optimization and solving nonlinear equation system,

but at first step of testing NLP gams solver, I have a trouble with solving the following code has been written in GAMS to solve one unknown-one equation system:


\

  • a hydrocarbon mixture with the following overall composition is flashed in a
  • separator at 50 psia and 100 F
    set i components /c3,ic4,nc4,ic5,nc5,c6/;
    alias (i,j);
    scalar ptotal,T;
    ptotal=50;T=100;
    ===============================================================================
    parameter Z(i) overall composition
    /c3 0.20
    ic4 0.10
    nc4 0.10
    ic5 0.20
    nc5 0.20
    c6 0.20/;
    Z(i)=z(i)/sum(j,z(j));
    parameter psat(i) vapor pressure at T from cox chart
    /c3 190
    ic4 72.2
    nc4 51.6
    ic5 20.44
    nc5 15.57
    c6 4.956/;
    parameter Kvalue(i);
    Kvalue(i)=psat(i)/Ptotal;
    display kvalue;
    ===============================================================================
    variable nv;
    equation E1;
    E1…sum( i, z(i)    (Kvalue(i)-1)/(nv    (Kvalue(i)-1))+1 ) =e=0;

parameter A,B;
A=sum(i,z(i)(Kvalue(i)-1));B=sum(i,z(i)(Kvalue(i)-1)/Kvalue(i));

model flash /All/;
nv.l=A/(A-B);
nv.lo=0;
nv.up=1;
*option nlp=minos
SOLVE flash USING nlp MINIMIZING nv;

How can I modify above code to solve it??



cheers

–
To unsubscribe from this group and stop receiving emails from it, send an email to gamsworld+unsubscribe@googlegroups.com.
To post to this group, send email to gamsworld@googlegroups.com.
Visit this group at http://groups.google.com/group/gamsworld.
For more options, visit https://groups.google.com/groups/opt_out.

–
To unsubscribe from this group and stop receiving emails from it, send an email to gamsworld+unsubscribe@googlegroups.com.
To post to this group, send email to gamsworld@googlegroups.com.
Visit this group at http://groups.google.com/group/gamsworld.
For more options, visit https://groups.google.com/groups/opt_out.