Nonlinear constraints with variables in the numerator of the fraction

GAMS
1

Hello all,

I have a problem with nonlinear objective function and constraints. The non linearity stems from a fraction which has variables in the denominator. hen I run the model, in the solution interface, it shows me a wrong format of the constraint. Im wondering if its just a representation or GAMS considers the constraint to be like this.

Example:

z(i)…sum(k,sum(j, x(k,i,j)*d(k,i))/sum(j,x(k,i,j))+10)

The solution interface shows me the constraint like this:

-x(k,i,j)*d(k,i,j) + x(k,i,j)

I belive in the above equation instead of showing “+” it should show me “/” but there is no sign of devision when it shows the constraint. Im really confused with this.

Thanks

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2

Hi Fateme



I assume that you take this from the listing of the equations.

The equation output is a correct representation of the algebraic structure of any linear terms in the equation and a local representation containing the first derivatives of any nonlinear terms. The nonlinear terms are automatically encased in parentheses to indicate a local approximation is present. See McCarls guide and search for „equations listing“.

Hope this helps



Cheers

Renger

Modelworks

Gewerbestrasse 15

3600 Thun – Switzerland

+41 79 818 53 73

Info@modelworks.ch

blog.modelworks.ch







From: gamsworld@googlegroups.com [mailto:gamsworld@googlegroups.com] On Behalf Of Fateme Fotuhi
Sent: Sonntag, 24. November 2013 01:13
To: gamsworld@googlegroups.com
Subject: Nonlinear constraints with variables in the numerator of the fraction



Hello all,



I have a problem with nonlinear objective function and constraints. The non linearity stems from a fraction which has variables in the denominator. hen I run the model, in the solution interface, it shows me a wrong format of the constraint. Im wondering if its just a representation or GAMS considers the constraint to be like this.



Example:



z(i)…sum(k,sum(j, x(k,i,j)*d(k,i))/sum(j,x(k,i,j))+10)



The solution interface shows me the constraint like this:



-x(k,i,j)*d(k,i,j) + x(k,i,j)



I belive in the above equation instead of showing “+” it should show me “/” but there is no sign of devision when it shows the constraint. Im really confused with this.



Thanks

–
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3

Thank you so much for the information.

On Saturday, November 23, 2013 7:13:07 PM UTC-5, Fateme Fotuhi wrote:

Hello all,

I have a problem with nonlinear objective function and constraints. The non linearity stems from a fraction which has variables in the denominator. hen I run the model, in the solution interface, it shows me a wrong format of the constraint. Im wondering if its just a representation or GAMS considers the constraint to be like this.

Example:

z(i)…sum(k,sum(j, x(k,i,j)*d(k,i))/sum(j,x(k,i,j))+10)

The solution interface shows me the constraint like this:

-x(k,i,j)*d(k,i,j) + x(k,i,j)

I belive in the above equation instead of showing “+” it should show me “/” but there is no sign of devision when it shows the constraint. Im really confused with this.

Thanks

–
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