Help in writing indexed equation

GAMS
1

Hi,

I am trying to write an indexed equation which runs over set i /1*4/.
How can a write just one equation and run an index to have all the
four equations.

the equation is

  1. Log( q(1)/Sum(q(i))) = alpha*P(2) + C + Log(q(1)/ q(1) + q(3))

  2. Log( q(2)/Sum(q(i))) = alpha*P(2) + C + Log(q(2)/ q(2) + q(4))

  3. Log( q(3)/Sum(q(i))) = alpha*P(3) + C + Log(q(3)/ q(1) + q(3))

  4. Log( q(4)/Sum(q(i))) = alpha*P(4) + C + Log(q(4)/ q(2) + q(4))

I tried defining C1, and C2 as subset of I. where C1 / 1, 3/ and C2 /
2, 4/ and then defining equation 1 and 3 over C1 and 2 and 4 over C2.

Set I / 1*4/
C1(I) /1, 3/
C2(I) /2, 4/;

Alias (I, J);

Eq1(C1)…

Log( q(C1)/Sum(J, q(J))) = alpha*P(C1) + C + Log(q(C1)/ Sum(C1, q
(C1))…this gives eq 1 and 3

similarly for C2 gives eq 2 and 4

I guess this works for this case but i want to know how can i pick and
choose which variables to have and which not to have in my equation
from a set. I know (ORD) and (not sameas) can work but in a random
equation with no pattern of subscript how can we pick and choose the
subscripts to have in the equation. If some can illustriate using the
above equations I will be highly obliged.

Thanks
Ashutosh

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2

I usually do this by using the dollar control option.

The syntax is: a(i)$(ord(i)=n)
where, ‘a’ is a variable or parameter defined over set ‘i’ and ‘n’ is the element of the set ‘i’ for which you want to write your equation.

I am not sure if this is the best approach but it works!

Hope this helps,

  • Yogendra.


    On Mon, Jul 13, 2009 at 8:30 PM, ashu wrote:


    Hi,

I am trying to write an indexed equation which runs over set i /1*4/.
How can a write just one equation and run an index to have all the
four equations.

the equation is

  1. Log( q(1)/Sum(q(i))) = alpha*P(1) + C + Log(q(1)/ q(1) + q(3))

  2. Log( q(2)/Sum(q(i))) = alpha*P(2) + C + Log(q(2)/ q(2) + q(4))

  3. Log( q(3)/Sum(q(i))) = alpha*P(3) + C + Log(q(3)/ q(1) + q(3))

  4. Log( q(4)/Sum(q(i))) = alpha*P(4) + C + Log(q(4)/ q(2) + q(4))

I tried defining C1, and C2 as subset of I. where C1 / 1, 3/ and C2 /
2, 4/ and then defining equation 1 and 3 over C1 and 2 and 4 over C2.

Set I / 1*4/
C1(I) /1, 3/
C2(I) /2, 4/;

Alias (I, J);

Eq1(C1)…

Log( q(C1)/Sum(J, q(J))) = alpha*P(C1) + C + Log(q(C1)/ Sum(C1, q
(C1))…this gives eq 1 and 3

similarly for C2 gives eq 2 and 4

I guess this works for this case but i want to know how can i pick and
choose which variables to have and which not to have in my equation
from a set. I know (ORD) and (not sameas) can work but in a random
equation with no pattern of subscript how can we pick and choose the
subscripts to have in the equation. If some can illustrate using the
above equations I will be highly obliged.

Thanks
Ashu



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3

Thanks Yogendra,

Just had a query, in this case it seems we will have to write multiple
equations and not a write a generic equation and run an index over it.
am i correct?..The index on the equation will keep on changing and so
i do not want to keep a fixed ‘n’. For example, i am trying to find a
way, if possible to write one equation to represent all of the above
four equations.

Thanks a lot for your help. Much appreciated.
Ashu

On Jul 14, 10:04 am, Yogendra Shastri wrote:

I usually do this by using the dollar control option.

The syntax is: a(i)$(ord(i)=n)
where, ‘a’ is a variable or parameter defined over set ‘i’ and ‘n’ is the
element of the set ‘i’ for which you want to write your equation.

I am not sure if this is the best approach but it works!

Hope this helps,

  • Yogendra.

On Mon, Jul 13, 2009 at 8:30 PM, ashu wrote:

Hi,

I am trying to write an indexed equation which runs over set i /1*4/.
How can a write just one equation and run an index to have all the
four equations.

the equation is

  1. Log( q(1)/Sum(q(i))) = alpha*P(1) + C + Log(q(1)/ q(1) + q(3))
  1. Log( q(2)/Sum(q(i))) = alpha*P(2) + C + Log(q(2)/ q(2) + q(4))
  1. Log( q(3)/Sum(q(i))) = alpha*P(3) + C + Log(q(3)/ q(1) + q(3))
  1. Log( q(4)/Sum(q(i))) = alpha*P(4) + C + Log(q(4)/ q(2) + q(4))

I tried defining C1, and C2 as subset of I. where C1 / 1, 3/ and C2 /
2, 4/ and then defining equation 1 and 3 over C1 and 2 and 4 over C2.

Set I / 1*4/
C1(I) /1, 3/
C2(I) /2, 4/;

Alias (I, J);

Eq1(C1)…

Log( q(C1)/Sum(J, q(J))) = alpha*P(C1) + C + Log(q(C1)/ Sum(C1, q
(C1))…this gives eq 1 and 3

similarly for C2 gives eq 2 and 4

I guess this works for this case but i want to know how can i pick and
choose which variables to have and which not to have in my equation
from a set. I know (ORD) and (not sameas) can work but in a random
equation with no pattern of subscript how can we pick and choose the
subscripts to have in the equation. If some can illustrate using the
above equations I will be highly obliged.

Thanks
Ashu
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4

Yes. That is right.
Unfortunately, I do not know how you can write this using a single equation. I suppose it will be through the use of subsets as you have tried before.

  • Yogendra.


    On Tue, Jul 14, 2009 at 1:34 PM, ashu wrote:


    Thanks Yogendra,

Just had a query, in this case it seems we will have to write multiple
equations and not a write a generic equation and run an index over it.
am i correct?..The index on the equation will keep on changing and so
i do not want to keep a fixed ‘n’. For example, i am trying to find a
way, if possible to write one equation to represent all of the above
four equations.

Thanks a lot for your help. Much appreciated.
Ashu

On Jul 14, 10:04 am, Yogendra Shastri wrote:

I usually do this by using the dollar control option.

The syntax is: a(i)$(ord(i)=n)
where, ‘a’ is a variable or parameter defined over set ‘i’ and ‘n’ is the
element of the set ‘i’ for which you want to write your equation.

I am not sure if this is the best approach but it works!

Hope this helps,

  • Yogendra.

On Mon, Jul 13, 2009 at 8:30 PM, ashu wrote:

Hi,

I am trying to write an indexed equation which runs over set i /1*4/.
How can a write just one equation and run an index to have all the
four equations.

the equation is

  1. Log( q(1)/Sum(q(i))) = alpha*P(1) + C + Log(q(1)/ q(1) + q(3))
  1. Log( q(2)/Sum(q(i))) = alpha*P(2) + C + Log(q(2)/ q(2) + q(4))
  1. Log( q(3)/Sum(q(i))) = alpha*P(3) + C + Log(q(3)/ q(1) + q(3))
  1. Log( q(4)/Sum(q(i))) = alpha*P(4) + C + Log(q(4)/ q(2) + q(4))

I tried defining C1, and C2 as subset of I. where C1 / 1, 3/ and C2 /
2, 4/ and then defining equation 1 and 3 over C1 and 2 and 4 over C2.

Set I / 1*4/
C1(I) /1, 3/
C2(I) /2, 4/;

Alias (I, J);

Eq1(C1)…

Log( q(C1)/Sum(J, q(J))) = alpha*P(C1) + C + Log(q(C1)/ Sum(C1, q
(C1))…this gives eq 1 and 3

similarly for C2 gives eq 2 and 4

I guess this works for this case but i want to know how can i pick and
choose which variables to have and which not to have in my equation
from a set. I know (ORD) and (not sameas) can work but in a random
equation with no pattern of subscript how can we pick and choose the
subscripts to have in the equation. If some can illustrate using the
above equations I will be highly obliged.

Thanks
Ashu



–~–~---------~–~----~------------~-------~–~----~
To post to this group, send email to gamsworld@googlegroups.com
To unsubscribe from this group, send email to gamsworld+unsubscribe@googlegroups.com
For more options, visit this group at http://groups.google.com/group/gamsworld?hl=en
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5

Thanks yogendra,

I will post on the group if i come across a solution to write a single
equation.

Thanks
Ashu

On Jul 15, 12:41 pm, Yogendra Shastri wrote:

Yes. That is right.
Unfortunately, I do not know how you can write this using a single equation.
I suppose it will be through the use of subsets as you have tried before.

  • Yogendra.

On Tue, Jul 14, 2009 at 1:34 PM, ashu wrote:

Thanks Yogendra,

Just had a query, in this case it seems we will have to write multiple
equations and not a write a generic equation and run an index over it.
am i correct?..The index on the equation will keep on changing and so
i do not want to keep a fixed ‘n’. For example, i am trying to find a
way, if possible to write one equation to represent all of the above
four equations.

Thanks a lot for your help. Much appreciated.
Ashu

On Jul 14, 10:04 am, Yogendra Shastri wrote:

I usually do this by using the dollar control option.

The syntax is: a(i)$(ord(i)=n)
where, ‘a’ is a variable or parameter defined over set ‘i’ and ‘n’ is the
element of the set ‘i’ for which you want to write your equation.

I am not sure if this is the best approach but it works!

Hope this helps,

  • Yogendra.

On Mon, Jul 13, 2009 at 8:30 PM, ashu wrote:

Hi,

I am trying to write an indexed equation which runs over set i /1*4/.
How can a write just one equation and run an index to have all the
four equations.

the equation is

  1. Log( q(1)/Sum(q(i))) = alpha*P(1) + C + Log(q(1)/ q(1) + q(3))
  1. Log( q(2)/Sum(q(i))) = alpha*P(2) + C + Log(q(2)/ q(2) + q(4))
  1. Log( q(3)/Sum(q(i))) = alpha*P(3) + C + Log(q(3)/ q(1) + q(3))
  1. Log( q(4)/Sum(q(i))) = alpha*P(4) + C + Log(q(4)/ q(2) + q(4))

I tried defining C1, and C2 as subset of I. where C1 / 1, 3/ and C2 /
2, 4/ and then defining equation 1 and 3 over C1 and 2 and 4 over C2.

Set I / 1*4/
C1(I) /1, 3/
C2(I) /2, 4/;

Alias (I, J);

Eq1(C1)…

Log( q(C1)/Sum(J, q(J))) = alpha*P(C1) + C + Log(q(C1)/ Sum(C1, q
(C1))…this gives eq 1 and 3

similarly for C2 gives eq 2 and 4

I guess this works for this case but i want to know how can i pick and
choose which variables to have and which not to have in my equation
from a set. I know (ORD) and (not sameas) can work but in a random
equation with no pattern of subscript how can we pick and choose the
subscripts to have in the equation. If some can illustrate using the
above equations I will be highly obliged.

Thanks
Ashu
–~–~---------~–~----~------------~-------~–~----~
To post to this group, send email to gamsworld@googlegroups.com
To unsubscribe from this group, send email to gamsworld+unsubscribe@googlegroups.com
For more options, visit this group at http://groups.google.com/group/gamsworld?hl=en
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