Hello,

I experience quite a strange behaviour of my two-stage MINLP

optimization model making use of the global solver BARON. The first

stage runs just fine, but the second one fails to find any solution,

because GAMS (or the solver?) automatically bounds the objective

variable with THE SAME values. I do not know why it is happening,

because all the variables have their bounds set prior to the SOLVE

statement. To be specific:

…

Option minlp = baron ;

$onecho > baron.opt

NumLoc 50

$offecho

ModelName.optfile = 1 ;

…

myVar.lo = 0 ;

myVar.up = 10000 ;

…

Solve ModelName using minlp minimizing myVar ;

When the solver finishes local search and starts to evaluate the

nodes, it logs:

Iteration Open Nodes Total Time Lower Bound Upper

Bound

1 1 000:00:02 0.800000D+04

0.800000D+04

and right after that – as can be expected – it stops with

Best solution found at node: -3

(i.e., no feasible solution found).

How is it possible that it sets completely different bounds for the

objective variable than I did and, moreover, how does it even come up

with the value 0.8e4???

Any help would be much appreciated.

nvx

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nvx,

The bound BARON produces is well within the bounds of your objective

variable, so everything is ok. The bound BARON provides comes from

solving a convex relaxation of your problem and this bound is

tightened by branching. You might want to post your model for further

analysis.

Regards,

Michael Bussieck - GAMSWorld Coordinator

On May 26, 2:20 pm, nvx wrote:

Hello,

I experience quite a strange behaviour of my two-stage MINLP

optimization model making use of the global solver BARON. The first

stage runs just fine, but the second one fails to find any solution,

because GAMS (or the solver?) automatically bounds the objective

variable with THE SAME values. I do not know why it is happening,

because all the variables have their bounds set prior to the SOLVE

statement. To be specific:

…

Option minlp = baron ;

$onecho > baron.opt

NumLoc 50

$offecho

ModelName.optfile = 1 ;

…

myVar.lo = 0 ;

myVar.up = 10000 ;

…

Solve ModelName using minlp minimizing myVar ;

When the solver finishes local search and starts to evaluate the

nodes, it logs:

Iteration Open Nodes Total Time Lower Bound Upper

Bound

1 1 000:00:02 0.800000D+04

0.800000D+04

and right after that – as can be expected – it stops with

Best solution found at node: -3

(i.e., no feasible solution found).

How is it possible that it sets completely different bounds for the

objective variable than I did and, moreover, how does it even come up

with the value 0.8e4???

Any help would be much appreciated.

nvx

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Dear Michael,

thank you very much for your response. I tried a few other (local)

solvers and all of them failed to find any feasible solution. I’ll

check the model again, maybe there is a typo there… I’ll post the

model here in case the problem should recur.

Best regards,

nvx

On 27 kvÄ›, 10:00, Gamsworld Admin wrote:

nvx,

The bound BARON produces is well within the bounds of your objective

variable, so everything is ok. The bound BARON provides comes from

solving a convex relaxation of your problem and this bound is

tightened by branching. You might want to post your model for further

analysis.

Regards,

Michael Bussieck - GAMSWorld Coordinator

On May 26, 2:20 pm, nvx wrote:

Hello,

I experience quite a strange behaviour of my two-stage MINLP

optimization model making use of the global solver BARON. The first

stage runs just fine, but the second one fails to find any solution,

because GAMS (or the solver?) automatically bounds the objective

variable with THE SAME values. I do not know why it is happening,

because all the variables have their bounds set prior to the SOLVE

statement. To be specific:

…

Option minlp = baron ;

$onecho > baron.opt

NumLoc 50

$offecho

ModelName.optfile = 1 ;

…

myVar.lo = 0 ;

myVar.up = 10000 ;

…

Solve ModelName using minlp minimizing myVar ;

When the solver finishes local search and starts to evaluate the

nodes, it logs:

Iteration Open Nodes Total Time Lower Bound Upper

Bound

1 1 000:00:02 0.800000D+04

0.800000D+04

and right after that – as can be expected – it stops with

Best solution found at node: -3

(i.e., no feasible solution found).

How is it possible that it sets completely different bounds for the

objective variable than I did and, moreover, how does it even come up

with the value 0.8e4???

Any help would be much appreciated.

nvx

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Problem solved!

There was a misplaced parenthesis in one of the equations. It is a

pity GAMS does not color-code parentheses or emphasize them in some

other way like modern language IDEs do…

Best regards,

nvx

On 27 kvÄ›, 10:55, nvx wrote:

Dear Michael,

thank you very much for your response. I tried a few other (local)

solvers and all of them failed to find any feasible solution. I’ll

check the model again, maybe there is a typo there… I’ll post the

model here in case the problem should recur.

Best regards,

nvx

On 27 kvÄ›, 10:00, Gamsworld Admin wrote:

nvx,

The bound BARON produces is well within the bounds of your objective

variable, so everything is ok. The bound BARON provides comes from

solving a convex relaxation of your problem and this bound is

tightened by branching. You might want to post your model for further

analysis.

Regards,

Michael Bussieck - GAMSWorld Coordinator

On May 26, 2:20 pm, nvx wrote:

Hello,

I experience quite a strange behaviour of my two-stage MINLP

optimization model making use of the global solver BARON. The first

stage runs just fine, but the second one fails to find any solution,

because GAMS (or the solver?) automatically bounds the objective

variable with THE SAME values. I do not know why it is happening,

because all the variables have their bounds set prior to the SOLVE

statement. To be specific:

…

Option minlp = baron ;

$onecho > baron.opt

NumLoc 50

$offecho

ModelName.optfile = 1 ;

…

myVar.lo = 0 ;

myVar.up = 10000 ;

…

Solve ModelName using minlp minimizing myVar ;

When the solver finishes local search and starts to evaluate the

nodes, it logs:

Iteration Open Nodes Total Time Lower Bound Upper

Bound

1 1 000:00:02 0.800000D+04

0.800000D+04

and right after that – as can be expected – it stops with

Best solution found at node: -3

(i.e., no feasible solution found).

How is it possible that it sets completely different bounds for the

objective variable than I did and, moreover, how does it even come up

with the value 0.8e4???

Any help would be much appreciated.

nvx

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Yes, better IDE support for would help in some cases. Currently, there

is F8 which moves the cursor to the matching parenthesis. I personally

prefer using different types of parenthesis. You can use ,(), and {}

anywhere parenthesis are used: sum{i,prod(j, a[i,j]*x[i,j])}

Michael Bussieck - GAMSWorld Coordinator

On May 28, 8:49 am, nvx wrote:

Problem solved!

There was a misplaced parenthesis in one of the equations. It is a

pity GAMS does not color-code parentheses or emphasize them in some

other way like modern language IDEs do…

Best regards,

nvx

On 27 kvÄ›, 10:55, nvx wrote:

Dear Michael,

thank you very much for your response. I tried a few other (local)

solvers and all of them failed to find any feasible solution. I’ll

check the model again, maybe there is a typo there… I’ll post the

model here in case the problem should recur.

Best regards,

nvx

On 27 kvÄ›, 10:00, Gamsworld Admin wrote:

nvx,

The bound BARON produces is well within the bounds of your objective

variable, so everything is ok. The bound BARON provides comes from

solving a convex relaxation of your problem and this bound is

tightened by branching. You might want to post your model for further

analysis.

Regards,

Michael Bussieck - GAMSWorld Coordinator

On May 26, 2:20 pm, nvx wrote:

Hello,

I experience quite a strange behaviour of my two-stage MINLP

optimization model making use of the global solver BARON. The first

stage runs just fine, but the second one fails to find any solution,

because GAMS (or the solver?) automatically bounds the objective

variable with THE SAME values. I do not know why it is happening,

because all the variables have their bounds set prior to the SOLVE

statement. To be specific:

…

Option minlp = baron ;

$onecho > baron.opt

NumLoc 50

$offecho

ModelName.optfile = 1 ;

…

myVar.lo = 0 ;

myVar.up = 10000 ;

…

Solve ModelName using minlp minimizing myVar ;

When the solver finishes local search and starts to evaluate the

nodes, it logs:

Iteration Open Nodes Total Time Lower Bound Upper

Bound

1 1 000:00:02 0.800000D+04

0.800000D+04

and right after that – as can be expected – it stops with

Best solution found at node: -3

(i.e., no feasible solution found).

How is it possible that it sets completely different bounds for the

objective variable than I did and, moreover, how does it even come up

with the value 0.8e4???

Any help would be much appreciated.

nvx

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Dear Michael,

thank you for this great tip! I did not know I can use other types of

parentheses/brackets – perhaps because I usually use programming

languages where every type of parentheses or brackets has different

purpose. (Note to self: be more curious next time and

experiment… )

Best regards,

nvx

On 28 kvÄ›, 14:57, Gamsworld Admin wrote:

Yes, better IDE support for would help in some cases. Currently, there

is F8 which moves the cursor to the matching parenthesis. I personally

prefer using different types of parenthesis. You can use ,(), and {}

anywhere parenthesis are used: sum{i,prod(j, a[i,j]*x[i,j])}

Michael Bussieck - GAMSWorld Coordinator

On May 28, 8:49 am, nvx wrote:

Problem solved!

There was a misplaced parenthesis in one of the equations. It is a

pity GAMS does not color-code parentheses or emphasize them in some

other way like modern language IDEs do…

Best regards,

nvx

On 27 kvÄ›, 10:55, nvx wrote:

Dear Michael,

thank you very much for your response. I tried a few other (local)

solvers and all of them failed to find any feasible solution. I’ll

check the model again, maybe there is a typo there… I’ll post the

model here in case the problem should recur.

Best regards,

nvx

On 27 kvÄ›, 10:00, Gamsworld Admin wrote:

nvx,

The bound BARON produces is well within the bounds of your objective

variable, so everything is ok. The bound BARON provides comes from

solving a convex relaxation of your problem and this bound is

tightened by branching. You might want to post your model for further

analysis.

Regards,

Michael Bussieck - GAMSWorld Coordinator

On May 26, 2:20 pm, nvx wrote:

Hello,

I experience quite a strange behaviour of my two-stage MINLP

optimization model making use of the global solver BARON. The first

stage runs just fine, but the second one fails to find any solution,

because GAMS (or the solver?) automatically bounds the objective

variable with THE SAME values. I do not know why it is happening,

because all the variables have their bounds set prior to the SOLVE

statement. To be specific:

…

Option minlp = baron ;

$onecho > baron.opt

NumLoc 50

$offecho

ModelName.optfile = 1 ;

…

myVar.lo = 0 ;

myVar.up = 10000 ;

…

Solve ModelName using minlp minimizing myVar ;

When the solver finishes local search and starts to evaluate the

nodes, it logs:

Iteration Open Nodes Total Time Lower Bound Upper

Bound

1 1 000:00:02 0.800000D+04

0.800000D+04

and right after that – as can be expected – it stops with

Best solution found at node: -3

(i.e., no feasible solution found).

How is it possible that it sets completely different bounds for the

objective variable than I did and, moreover, how does it even come up

with the value 0.8e4???

Any help would be much appreciated.

nvx

–~–~---------~–~----~------------~-------~–~----~

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