## Search found 85 matches

- 3 weeks ago
- Forum: Modeling
- Topic: linearization of a logarithmic function (log) defined over a variable
- Replies:
**1** - Views:
**172**

### Re: linearization of a logarithmic function (log) defined over a variable

Hi, the logarithmic function is a concave function so you can overestimate the function with first order Taylor approximations in domain points or underestimate using a piecewise linear approximation.

- 2 months ago
- Forum: Syntax
- Topic: How to write this constraint in GAMS Code?
- Replies:
**3** - Views:
**229**

### Re: How to write this constraint in GAMS Code?

Hi, I guess you have to define the set, subset and alias.

for example:

for example:

Code: Select all

```
sets
i /i1*i10/
v /v1*v10/
N0(i) /i1,i3,i4,i5/
;
alias(i,j);
eq(i,v)$N0(i).. sum(j$(N0(j) and ord(j) ne ord(i)),x(i,j,v)) =e= sum(j$(N0(j) and ord(j) ne ord(i)),x(j,i,v))
```

### Re: Loop

Hi, do you need the loop to define a parameter or is it an equation? No loops are used to define equations. anyway, you don't need a loop for this definition. as a equation: set i /1*13/ ; alias(i,j,k) eq(i).. log(gamma(i)) =e= - A*power(z(i),2) + 2*sum(j$(ord(j) ne ord(i)),m(j)*(B_0(i,j) + B_1(i,j)...

- 7 months ago
- Forum: Syntax
- Topic: logical equations & binary variables
- Replies:
**18** - Views:
**3301**

### Re: logical equations & binary variables

Hi, in the previous answer I wrote this code and I saved it as a draft. I hope this can help you. Bye! set i intervals /i1*i6/ n your nset /n1*n2/ l limits /l,u/ ; parameter p(n) /n1 1, n2 3/ intervals(n,i,l) anvalue(i) /i1 0 i2 0.2 i3 0.4 i4 0.6 i5 0.8 i6 1/ evalue /1e-6/ ; intervals(n,'i1','l')=0;...

- 8 months ago
- Forum: Syntax
- Topic: logical equations & binary variables
- Replies:
**18** - Views:
**3301**

### Re: logical equations & binary variables

Hi, if p (n) is a parameter, I think it is better to reformulate the intervals definition: if th >= p(n) then a(n) =0; else if th < p(n) and th >= p(n) * 10^-.5 then a(n) = .2; else if th < p(n)*10^-.5 and th >= p(n) * 10^-1 then a(n) = .4; else if th < p(n)*10^-1 and th >= p(n) * 10^-1.5 then a(n) ...

- 8 months ago
- Forum: Tools
- Topic: Generate an array of random numbers
- Replies:
**6** - Views:
**612**

### Re: Generate an array of random numbers

I did not know the shuffle option. Thanks for sharing dirkse!

- 8 months ago
- Forum: Tools
- Topic: Generate an array of random numbers
- Replies:
**6** - Views:
**612**

### Re: Generate an array of random numbers

Hi dirkse, i like your compact implementation.

I tested your code but sometimes I got less than seven items with a value of 1 and sometimes more.

i'm right?

I tested your code but sometimes I got less than seven items with a value of 1 and sometimes more.

i'm right?

- 8 months ago
- Forum: Tools
- Topic: Generate an array of random numbers
- Replies:
**6** - Views:
**612**

### Re: Generate an array of random numbers

Hi, this is a good challenged! I think this can work. *reset the seed for the random number generator. execseed = 1 + gmillisec(jnow); Set W /1*10/ select(W); alias(W,Wp); select(W)=NO; Parameter Coef(W) p A /70/ ; loop(W$(ord(w) le floor(A*card(W)/100)), p = uniformInt(1,card(W)); while( sum(Wp$(or...

- 8 months ago
- Forum: Syntax
- Topic: Index change for constraints
- Replies:
**4** - Views:
**453**

### Re: Index change for constraints

Ok, you must start with the second value of i

eq(i)$(ord(i) ge 2).. T(i) =g= T(i-1);

Bye!

eq(i)$(ord(i) ge 2).. T(i) =g= T(i-1);

Bye!

- 8 months ago
- Forum: Syntax
- Topic: Index change for constraints
- Replies:
**4** - Views:
**453**

### Re: Index change for constraints

Hi, Is T a binary or continuous variable?

Is "T(i)" greater (>) or greater than or equal (>=) than "T(i-1)" ?

Bye

Is "T(i)" greater (>) or greater than or equal (>=) than "T(i-1)" ?

Bye