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## Re: [Help-glpk] power of: calculate 2^x from variable x

 From: malekro Subject: Re: [Help-glpk] power of: calculate 2^x from variable x Date: Tue, 7 Jun 2011 19:12:02 -0700 (PDT)

```i forgot to mention that the values of x are < card(C). this is guaranteed
and required for this to work.

malekro wrote:
>
> hello,
>
> i am trying to calculate 2^x from a variable x. i already spent several
> hours and with the help of archived posts i thought i have the solution.
> unfortunately i cannot figure out why the code below returns an empty
> result or malforms the x variable, i think the idea is correct.
>
> set R := {0..3};
> set C := {0..2};
>
> # the given numbers that need to be powered by 2
> var x{R}, integer;
>
> # temporary table, each row will later be used for multiplication with 2^c
> var t{R,C}, binary;
>
> # the desired solution 2^x
> var s{R}, integer;
>
> # set the x-th cell in temporary row to 1, rest 0
> s.t. c1{r in R}: sum{c in C} t[r,c] = 1; # exactly one 1 in row
> s.t. c3{r in R, c in C}: c * t[r,c] = x[r]; # set the x[r]-th cell to 1
> s.t. c2{r in R}: sum{c in C} c * t[r,c] = x[r]; # verification so t[r,0]
> != 1 if x[r] > 0
>
> # multiply the c-th cell of the temporary row with 2^c
> s.t. c4{r in R}: s[r] = sum{c in C} (2 ** c) * t[r,c];
>
>
> i would be grateful for any help.
>
> thanks,
> manuel
>

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