trigonometric functions
trigonometric functions
Hi friends, I have some problems in programming some equations in gams, I am new using gams and I donâ€™t have very clear how to program equation with trigonometric functions.
One of the equations that I am having problems with is this:
P=âˆ‘ Vi*Vj*(Gij*cos(OiOj)+Bij*sin(OiOj))
j=1
The tutorial says that gams Currently have no support for other functions, including the trigonometric functions cos(x),sin(x), etc.

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Re: trigonometric functions
GAMS does support the math functions you have identified. Go to the McCarl's guide and search on functions and select Other Mathematical functions and you will see a broad list of supported math functions. You can calculate these values using gams outside of an optimization model, however if you are using the equation inside the optimization you will need a non linear solver.
When we have problems of these types we usually calculate these equations in the premodel for all possible combinations and then write an optimization to select the values that either minimize or maximize the objective function. Then you can use a traditional solver which is always a lot faster than a non linear solver approach.
Regards,
John
On Tue, Jan 6, 2015 at 11:33 AM, asier bernardo mugarra flores wrote:
Hi friends, I have some problems in programming some equations in gams, I am new using gams and I donâ€™t have very clear how to program equation with trigonometric functions.
One of the equations that I am having problems with is this:
P=âˆ‘ Vi*Vj*(Gij*cos(OiOj)+Bij*sin(OiOj))
j=1
The tutorial says that gams Currently have no support for other functions, including the trigonometric functions cos(x),sin(x), etc.

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To post to this group, send email to gamsworld@googlegroups.com.
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For more options, visit https://groups.google.com/d/optout.

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Re: trigonometric functions
For Power Flow Equation best internet resource for GAMS is
https://www.princeton.edu/~rvdb/ampl/nl ... index.html
best regards
Abraham
On Tue, Jan 6, 2015 at 9:33 PM, asier bernardo mugarra flores wrote:
Hi friends, I have some problems in programming some equations in gams, I am new using gams and I donâ€™t have very clear how to program equation with trigonometric functions.
One of the equations that I am having problems with is this:
P=âˆ‘ Vi*Vj*(Gij*cos(OiOj)+Bij*sin(OiOj))
j=1
The tutorial says that gams Currently have no support for other functions, including the trigonometric functions cos(x),sin(x), etc.

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To post to this group, send email to gamsworld@googlegroups.com.
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 User
 Posts: 17
 Joined: 8 months ago
Re: trigonometric functions
Hi, I was studding in how to implement trigonometric functions.
I founded this site, about Extrinsic Functions.
https://www.gams.com/latest/docs/UG_Ext ... aryExample
I need to use the angle with radian unit. So at GAMS website they suggest to use Function Libraries, an example, trilib01.gms , trilib02.gms and trilib03.gms .
https://www.gams.com/latest/testlib_ml/ ... lib01.html C
https://www.gams.com/latest/testlib_ml/ ... lib02.html Delphi
https://www.gams.com/latest/testlib_ml/ ... lib03.html Fortran
But how I suppose to use this examples in my mproblem.
Is just save in my folder, or a specific folder?
What the difference of using:
or
??
Tnks
I founded this site, about Extrinsic Functions.
https://www.gams.com/latest/docs/UG_Ext ... aryExample
I need to use the angle with radian unit. So at GAMS website they suggest to use Function Libraries, an example, trilib01.gms , trilib02.gms and trilib03.gms .
https://www.gams.com/latest/testlib_ml/ ... lib01.html C
https://www.gams.com/latest/testlib_ml/ ... lib02.html Delphi
https://www.gams.com/latest/testlib_ml/ ... lib03.html Fortran
But how I suppose to use this examples in my mproblem.
Is just save in my folder, or a specific folder?
What the difference of using:
Code: Select all
Function <InternalFuncName> /<InternalLibName>.<FuncName>/;
Code: Select all
$ifThen set nocomp
* Use precompiled library provided by testlib
$ batinclude precomp.inc tricclib
$else
* Compile library from source code
$ batinclude compilec.inc tri
$endIf
function myCos / myLib.Cosine /
mySin / myLib.Sine /
myPi / myLib.Pi /;
Tnks

 User
 Posts: 87
 Joined: 3 years ago
 Location: Rosario  Argentina
Re: trigonometric functions
GAMS supports trigonometric functions.
What are the functions you have problems with?
Extrinsic functions are to implements your own functions.
Best
What are the functions you have problems with?
Extrinsic functions are to implements your own functions.
Best

 User
 Posts: 17
 Joined: 8 months ago
Re: trigonometric functions
Manassaldi wrote: ↑1 month agoGAMS supports trigonometric functions.
What are the functions you have problems with?
Extrinsic functions are to implements your own functions.
Best
My problems is with this equation:
Code: Select all
* Diameter for each tube with flow
dred(a).. dr(a) =e= vcPower((abc1(a)*man*qr(a)/sqrt(ir(a))),(3/8));
eq1(a).. abc1(a) =e= vcPower(3.0844*theta(a),(1/4))/abc2(a);
eq2(a).. abc2(a) =e= vcPower((theta(a)  sin(theta(a))),(5/8));
Error at line ....: division by zero (0)
than I tried to insert a condition "$(theta(a) gt 0)":
Code: Select all
* Diameter for each tube with flow
dred(a).. dr(a) =e= vcPower((abc1(a)*man*qr(a)/sqrt(ir(a))),(3/8));
eq1(a).. abc1(a)$(theta(a) gt 0) =e= vcPower(3.0844*theta(a),(1/4))/abc2(a);
eq2(a).. abc2(a)$(theta(a) gt 0) =e= vcPower((theta(a)  sin(theta(a))),(5/8));
this code not work even of I used "$(qn(a) gt 0)" to indicate if the tube have flow or not.
a error appear:
Endogenous $ operation not allowed
I'm using :
Code: Select all
Solve network using MINLP minimizing cost

 User
 Posts: 87
 Joined: 3 years ago
 Location: Rosario  Argentina
Re: trigonometric functions
That is not a GAMS valid sentence. Maybe you are confused in the way "GAMS" works. I think i can't help you
Best
Best
Re: trigonometric functions
Hi
This might be resolved by setting a starting value that is not equal to zero. If you don't set a starting value for your variables, Gams assumes zero.
You could for example set THETA.L = 1;
Cheers
Renger
This might be resolved by setting a starting value that is not equal to zero. If you don't set a starting value for your variables, Gams assumes zero.
You could for example set THETA.L = 1;
Cheers
Renger
____________________________________
Enjoy modeling even more: Read my blog on modeling at The lazy economist
Enjoy modeling even more: Read my blog on modeling at The lazy economist

 User
 Posts: 17
 Joined: 8 months ago