Re: [Help-glpk] fraction with vars

[Kasper Tordrup]

Hi again guys

After looking over Xypron's example, it became clear to me that you lack some information, sorry for that.

The x represent a percentage of p that I need, and this means that y is <= to w.

So summing up:

x will always be <= to p.

y will always be <= to w.

if w is 0, then so are y.

p is a constant.

x,y and w are variables.

y and w are in the range [0..6] (or close to that)

and I want to calculate:

x_suj = p_s * (y_suj/w_su)

Sorry for the mess, hope this clarifies it.

Best regards,

Kasper

On Wed, May 2, 2012 at 9:03 AM, Kasper Tordrup <address@hidden> wrote:

Hi guys
Thanks for all the answers, I haven't had much time to look at them.

However I can tell you that the range of y and w are both [0..6] maybe a little higher. And if w is 0, then so are y.

Maybe this helps a little.

Best regards,

Kasper

On Apr 29, 2012 5:23 AM, "Michael Hennebry" <address@hidden> wrote:

Divisiblilty can be used to reduce the problem somewhat.

On Fri, 27 Apr 2012, Michael Hennebry wrote:

# Solve
# x = p * y / w
# w * pd * x = pn * y
# where x, y, w are natural numbers and
# p = 11 / 17
# pn = 11
# pd = 17
# x in [23, 100]
# y in [10, 200]
# w in [3, 7]

# Since pn/pd is in lowest terms, y must be a multiple of pd.

param w_min := 3;
param w_max := 7;

param pn := 11;
param pd := 17;

set I := {w_min..w_max};

var w{I}, binary;
var y, integer, >= 10, <= 200;
var x, integer, >= 23, <= 100;

var ypd, integer, >= 10/pd, <= 200/pd
#                     1         11
s.t. y_formula :
   y = ypd*pd;

s.t. lb{i in I} :
  i * pd * x >= pn * y - (1-w[i]) * (pn*200-i*pd*23);

    i   *    x >= pn*ypd - (1-w[i]) * (pn*11 -i*   23);

s.t. ub{i in I} :
  i * pd * x <= pn * y + (1-w[i]) * (i*pd*100-pn*10);

    i   *    x <= pn*ypd + (1-w[i]) * (i *  100-pn   );

s.t. sm :
  sum{i in I} w[i] = 1;

solve;

printf "x = %f\ny = %f\nw = %f\n", x, y, sum{i in I} w[i] * i;

end;

--
Michael   address@hidden
"On Monday, I'm gonna have to tell my kindergarten class,
whom I teach not to run with scissors,
that my fiance ran me through with a broadsword."  --  Lily

--

Kasper Tordrup - Stud. M. Sc.
IMADA @ University of Southern Denmark
address@hidden - +45 27 44 58 49