Re: One-off error in the MIP solver?

[Domingo Alvarez Duarte]

Hello Harmut !

Testing it on https://meimporta.eu/myglpk-ext/ that's GLPK 4.65 plus 
several customizations gives this result:

===

v: 131072
v: 00011111111111111111
v: 131071
e: 0

===

I'm don't see a reason to upgrade right now.

Cheers !

On 24/1/22 10:46, Hartmut Henkel wrote:
> Hi,
>
> here seems to be some one-off error in gmpl/glpk (5.0, debian Linux):
>
> param v := 131072;
> param n := 20; # number of bits
> set J  := 1..n; # set of all bits
> var x{j in J}, binary;
> var e, >= 0;
> minimize slack: e;
>
> s.t. cs1: sum{j in J} (2**(j - 1) * x[j]) - v <=  e;
> s.t. cs2: sum{j in J} (2**(j - 1) * x[j]) - v >= -e;
>
> solve;
>
> printf "v: %d\nv: ", v;
> for {j in J} printf "%d", x[n - j + 1];
> printf "\n";
> printf "v: %d\n", sum{j in J} (2**(j - 1) * x[j]);
> printf "e: %d\n", e;
>
> end;
>
> Here it prints:
>
> v: 131072
> v: 0011111111111111111
> v: 131071
> e: 0
>
> With v = 131071 or v = 131073 or v = 65536 it works fine. Also fine with
> larger numbers like v = 888888. Same problem when solving the exported
> .lp file, which looks ok., confirmed by another solver. Seems not to be
> a general int limitation or printing issue. Do you have any idea what's
> happening here?
>
> Best Regards, Hartmut