Hello guys, i would like to know how to do the coding for the equation section if i want to let the model automatically let the positive value of NVS equals to “LVS” and negative value of NVS equals to -ULVS/0.9. And how to do the coding for CVS? Many thanks!

Looks like all these are parameters. You don’t need =e= type equations for this. This are simply assignments like you do in a normal program.

what do you mean by “positive value of NVS equal to “LVS”” if you already have a value, do you want to reset it? Do you already have values for NVS?
If so,
NVS(i,d)$(NVS(i,d) > 0) = LVS(i,d);

NVS(i,d)$(NVS(i,d) < 0) = -ULVS(i,d)/0.9;

If all of these are not parameters, then your question does not make sense because variables don’t have values. They have values only after solve.

Hi, i do realised that should be put under parameter too! However, i would required to use some variables obtain from the equation section and put in the parameter section, but then the error shows “a suffix is missing…”

After solve, variables have much more information than just the solution. They have (.l, .lo, .up, .scale, .m). Please take a look at variable attributes for more details: https://www.gams.com/latest/docs/UG_Variables.html#UG_Variables_VariableAttributes
When you just write variablename, GAMS does not understand which one of these you really want. This is why you get suffix is missing error. You should use .l

Good day, after i code LVS and ULVS under parameter, and added suffix to the variable, it showed Symbol declared but no values have been assigned. Is it because i code the parameter section at wrong sequence??

$onuellist
Set
i supply /i1*i2/
j demand /j1/
d number of days in a time cycle /d1*d7/
OW organic waste 1=swine manure 2=rice straw /OW1*OW2/
*VSS daily volatile solid supply
;
Parameter MFi(i) mass flow of supply
*i1=swine manure; i2=rice straw;
/
i1 99
i2 99
/
;
Parameter MFj(j) mass flow of demand
*j1=methane
/
j1 20
/
;
Parameter CNi(i) CN of supply
*i1=swine manure;
*i2=rice straw;
/
i1 15.8
i2 44.1
/
;
Parameter CNj(j) CN of demand
*j1=methane
/
j1 27.4
/
;
Parameter j1_kWh(d) daily energy demand per house @kWh
/
d1 22
d2 23
d3 21
d4 23
d5 22
d6 25.5
d7 25.8
/
;
Parameter dummy(d) daily energy demand per house @kWh
/
d1 1
d2 1
d3 1
d4 1
d5 1
d6 1
d7 1
/
;
*Parameter VSS1(d) daily VS for supply 1
*/
*d1 204
*d2 132
*d3 120
*d4 156
*d5 132
*d6 59
*d7 34
*/
*;
*Parameter VSS2(d) daily VS for supply 2
*/
*d1 299
*d2 325
*d3 286
*d4 273
*d5 338
*d6 0
*d7 0
*/
*;
*Table VSS(d,i) daily Volatile solid supply
* i1 i2
*d1 204 299
*d2 132 325
*d3 120 286
*d4 156 273
*d5 132 338
*d6 59 0
*d7 34 0
*;
Table VSS(i,d) daily Volatile solid supply
d1 d2 d3 d4 d5 d6 d7
i1 204 132 120 156 132 59 32
i2 299 325 286 273 338 0 0
;
Parameter TS(i) total solid percentage
/
i1 30.4
i2 92.9
/
;
Parameter C(i) carbon in the total solid percentage
/
i1 34.8
i2 39.7
/
;
Parameter H(i) hydrogen in the total solid percentage
/
i1 4.7
i2 5.4
/
;
Parameter O(i) oxygen in the total solid percentage
/
i1 30.3
i2 38.2
/
;
Parameter N(i) nitrogen in the total solid percentage
/
i1 2.2
i2 0.9
/
;
Parameter Other(i) other components in the total solid percentage
/
i1 28
i2 15.8
/
;
Parameter CN(i) CN ratio
/
i1 15.8
i2 44.1
/
;
Parameter VS(i) volatile solid in the total solid percentage
/
i1 22
i2 81.6
/
;
Parameter
Ci(i) C of supply,Cj(j) C of demand,
Ni(i) N of supply,Nj(j) N of demand
;
Ci(i)=[CNi(i)/(CNi(i)+1)]*MFi(i);
Cj(j)=CNj(j)/(CNj(j)+1)*MFj(j);
Ni(i)=MFi(i)-Ci(i);
Nj(j)=MFj(j)-Cj(j);
Scalar
Unit unit of houses /50/
CN_ch4 CN ratio required by methane /27.4/
Cmw carbon molecular weight /12/
Hmw hydrogen molecular weight /1/
Omw oxygen molecular weight /16/
Nmw nitrogen molecular weight /14/
;
Parameter
j50_kWh(d) total daily energy demand for 50 houses @kWh,
j_ch4 equivalent of methane demand for 50 houses @m3 CH4,
p_m4 average production of methane
p_ch4 daily production of methane,
n_ch4 daily net methane,
c_ch4 daily methane cumulative
;
j50_kWh(d)=j1_kWh(d)*50;
j_ch4(d)=j50_kWh(d)/10;
p_m4=sum[d,j_ch4(d)]/7;
p_ch4(d) = p_m4*dummy(d);
n_ch4(d)=p_ch4(d)-j_ch4(d);
c_ch4('d1')=p_ch4('d1')-j_ch4('d1');
c_ch4('d2')=c_ch4('d1')+p_ch4('d2')-j_ch4('d2');
c_ch4('d3')=c_ch4('d2')+p_ch4('d3')-j_ch4('d3');
c_ch4('d4')=c_ch4('d3')+p_ch4('d4')-j_ch4('d4');
c_ch4('d5')=c_ch4('d4')+p_ch4('d5')-j_ch4('d5');
c_ch4('d6')=c_ch4('d5')+p_ch4('d6')-j_ch4('d6');
c_ch4('d7')=c_ch4('d6')+p_ch4('d7')-j_ch4('d7');
*c_ch4(d)=C_ch4(d-1)+p_ch4(d)-j_ch4(d);
Variable
OF Objective function
NVS Net VS
MFij Mass flowrate from supply to demand
Frij(i,j) Fraction of supply to demand
;
Positive variable
Cij Carbon from supply to demand
Nij Nitrogen from supply to demand
Hij Hydrogen from supply to demand
Oij Oxygen from supply to demand
Otherij Other from supply to demand
Cmole Carbon mole received by each demand
Hmole Hydrogen mole received by each demand
Omole Oxygen mole received by each demand
Nmole Nitrogen mole received by each demand
TP_ch4 Theoretical ch4 production based on the feedstock composition
TP_co2 Theoretical co2 production based on the feedstock composition
TP_nh3 Theoretical nh3 production based on the feedstock composition
TA_fac Theoretical-actual factor for the production
AP_co2 Actual co2 production based on the feedstock composition
AP_nh3 Actual nh3 production based on the feedstock composition
Biogas_s Biogas storage capacity
TVS TOtal vs demand
TVSD Daily Total VS demand
IVS Individual VS demand
IVSD Daily Individual VS demand
CVS Cumulative VS
CVSmax maximum cumulative VS
y individual mass percentage of supply
;
Equation
Eq1 Total MF of supply must equal or less than supply to demand
Eq2a Sending C and N simultaneously from supply to demand side
Eq2b Sending C and N simultaneously from supply to demand side
Eq2c Sending C and N simultaneously from supply to demand side
Eq2d Sending H from supply to demand side
Eq2e Sending O from supply to demand side
Eq2f Sending other components from supply to demand side
Eq3 Total fraction used for each supply must less than 1
Eq4a Sum of demand MF must equal to sum of supply and external supply
Eq4b Sum of demand C must equal to sum of supply and external supply
Eq4c Sum of demand N must equal to sum of supply and external supply
Eq0F OF minimize the utilization of ES
Eq5a Carbon mole received by each supply
Eq5B Hydrogen mole received by each supply
Eq5C Oxygen mole received by each supply
Eq5D Nitrogen mole received by each supply
Eq6a Theoretical CH4 production @ m3 per kg VS
Eq6b Theoretical CO2 production @ m3 per kg VS
Eq6c Theoretical NH3 production @ m3 per kg VS
Eq7a Actual CH4 production @ m3 per kg VS
Eq7b Actual CO2 production @ m3 per kg VS
Eq7c Actual NH3 production @ m3 per kg VS
Eq7d Biogas storage capacity
Eq8a total VS demand
Eq8b daily total VS demand
Eq8c individual VS demand
Eqy mass percentage
Eq8d daily Individual VS demand
Eq8NVS daily net VS
Eq8e cumulative VS
Eq8f cumulative VS
*Eq9a CVSmax
*Eq9b OW storage
;
Eq1(i).. (MFi(i))=G=sum[(j),MFij(i,j)];
Eq2a(i,j).. MFij(i,j) =E=(Frij(i,j))*[Ci(i)+Ni(i)];
Eq2b(i,j).. Cij(i,j) =E= Frij(i,j)*Ci(i);
Eq2c(i,j).. Nij(i,j) =E= Frij(i,j)*Ni(i);
Eq2d(i,j).. Hij(i,j) =E= [H(i)/C(i)]*[Cij(i,j)];
Eq2e(i,j).. Oij(i,j) =E= [O(i)/C(i)]*[Cij(i,j)];
Eq2f(i,j).. Otherij(i,j) =E=[Other(i)/C(i)]*[Cij(i,j)];
Eq3(i,j).. Frij(i,j)=L=1;
Eq4a(j).. MFj(j)=E=sum[i,MFij(i,j)];
Eq4b(j).. Cj(j)=E=sum(i,Cij(i,j));
Eq4c(j).. Nj(j)=E=sum(i,Nij(i,j));
Eq5a(j).. Cmole(j)=E=sum[i,Cij(i,j)]/Cmw;
Eq5b(j).. Hmole(j)=E=sum[i,Hij(i,j)]/Hmw;
Eq5c(j).. Omole(j)=E=sum[i,Oij(i,j)]/Omw;
Eq5d(j).. Nmole(j)=E=sum[i,Nij(i,j)]/Nmw;
Eq6a(j).. TP_ch4(j)*[12*Cmole(j)+Hmole(j)+16*Omole(j)+14*Nmole(j)]=E={22.4*[0.5*Cmole(j)+0.125*Hmole(j)-0.25*Omole(j)-0.375*Nmole(j)]*0.8};
Eq6b(j).. TP_co2(j)*[12*Cmole(j)+Hmole(j)+16*Omole(j)+14*Nmole(j)]=E={22.4*[0.5*Cmole(j)-0.125*Hmole(j)+0.25*Omole(j)+0.375*Nmole(j)]*0.8};
Eq6c(j).. TP_nh3(j)*[12*Cmole(j)+Hmole(j)+16*Omole(j)+14*Nmole(j)]=E={22.4*Nmole(j)*0.8};
Eq7a.. TA_fac*sum(j,TP_ch4(j))=E=[smax(d,c_ch4(d))];
Eq7b(j).. AP_co2(j)=E=TP_co2(j)*TA_fac;
Eq7c(j).. AP_nh3(j)=E=TP_nh3(j)*TA_fac;
Eq7d(j).. Biogas_S(j)=E=[smax(d,c_ch4(d))]+AP_co2(j)+AP_nh3(j);
Eq8a.. TVS*sum(j,TP_ch4(j))=E=sum[d,p_ch4(d)]/7;
Eq8b(d).. TVSD(d)=E=TVS*dummy(d);
Eq8c(i,j).. IVS(i,j) =E= [Cij(i,j)+Hij(i,j)+Oij(i,j)+Nij(i,j)+Otherij(i,j)];
Eqy(i,j).. y(i,j)*{IVS('i1',j)+IVS('i2',j)}=E= IVS(i,j);
Eq8d(i,d).. IVSD(i,d) =E=sum(j,y(i,j))*TVSD(d);
Eq8nvs(i,d).. NVS(i,d) =E= VSS(i,d)-IVSD(i,d);
Eq8e(i,d).. CVS(i,'d1')=E= VSS(i,'d1')-IVSD(i,'d1');
Eq8f(i,d).. CVS(i,d)=E= CVS(i,d-1)+[VSS(i,d)]-IVSD(i,d);
*Eq9a(i).. CVSmax(i) =E= smax(d,CVS(i,d))*1;
*Eq9b(i).. OWSS(i)*sum(i,TS(i))*sum(i,VS(i)) =E= sum(d,CVSmax(i,d));
Eq0F.. OF =E= sum[(i,j),MFij(i,j)]*1;
Parameter
LVS(i,d) VS loading,
ULVS(i,d) VS unloading
;
NVS.l(i,d)$(NVS.l(i,d) > 0) = LVS(i,d);
NVS(i,d)$(NVS(i,d) < 0) = -ULVS(i,d)/0.9;
Model abc /all/;
solve abc us dnlp max OF;
Display
MFi,MFj,MFij.l,
CNi,CNj,
Ci,Cj,Cij.l,
Ni,Nj,Nij.l,
Frij.L
*,OF.L,
MFi,CNi,Ci,Ni,
MFj,CNj,Cj,Nj,
MFij.l,Cij.l,Nij.l,Hij.l,Oij.l,Otherij.l,
Frij.L
*,OF.L,
j50_kWh,j_ch4,p_ch4,c_ch4,
Cmole.l,Hmole.l,Omole.l,Nmole.l,TP_ch4.l,TP_co2.l,TP_nh3.l,
TA_fac.l,AP_co2.l,AP_nh3.l,Biogas_s.L,TVSD.L,IVS.L,y.l,IVSD.L,NVS.l,VSS,CVS.L

There are many many fundamentally wrong things in this piece of code. Brings me back to my initial comment
“what do you mean by “positive value of NVS equal to “LVS”” if you already have a value, do you want to reset it? Do you already have values for NVS?”

Parameter
LVS(i,d) VS loading,
ULVS(i,d) VS unloading
;

When you say this you mean that you “know” the value of LVS and ULVS before you solve.

When you say that NVS depends on LVS, and by the above statement (i.e., you know LVS), you should also know NVS, therefore NVS should be a parameter as well.

Note that variables have values only “after” solve. So I don’t know what you want to do and it will be good for you to invest some time understanding the concepts of parameters and variables. So the following statement is meaningless because there are no .l values.
NVS.l(i,d)$(NVS.l(i,d) > 0) = LVS(i,d);

I don’t know what you want to model but I can confirm that this current logical sequence in your model is wrong.

Greetings! My bad as i wanna rush my things but thanks for pointing out my unseen/unpractical attitude in solving GAMS while not really understand all those fundamental. I had tried your method and finally solved my problem! Thanks again!