Re: Problems with NMaximize.

*To*: mathgroup at smc.vnet.net*Subject*: [mg69237] Re: Problems with NMaximize.*From*: Peter Pein <petsie at dordos.net>*Date*: Sun, 3 Sep 2006 01:39:39 -0400 (EDT)*References*: <ed6935$jie$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Nacho schrieb: > Hello. > > I'm trying to solve a real-life problem using Mathematica and I am > having some problems with NMaximize. > > As background, the problem is related to VDSL2 technology. The physical > frame can be configured using different parameters (primary parameters) > and those parameters defines the secondary parameters. > > I want Mathematica to maximize the datarate in the line while > maintaining some performance on the secondary parameters. > > Now, the formulas. > > I want to maximize the datarate, definded as: > > l*(nfec-r-1)*4000/nfec > ... > > Any help is welcomed to solve the problem. > > Thanks in advance. > > Regards. > Hello, I've got the impression, Mathematica doesn't like rational constraints, when using integer variables; but this may be wrong. I used Jean-Marc's tip for specifying the range for r and got: In[1]:= datarate = l*(nfec - r - 1)*(4000/nfec); constr = And @@ {d*r*i >= l*nfec, nfec == q*i, 0 <= (i - 1)*(d - 1) <= 8*l, 1000 <= l <= 23850, 1 <= q <= 8, 1 <= d <= 2048, 1 <= nfec <= 255, 0 <= r <= 8, {l, nfec, d, q, i, r} \[Element] Integers, Or @@ Thread[r == {0, 2, 4, 6, 8, 10, 12, 14, 16}]}; solution = NMaximize[{datarate, constr}, {r, l, nfec, d, q, i}] Out[3]= {1.24865*^7, {d -> 1924, i -> 16, l -> 3842, nfec -> 16, q -> 1, r -> 2}} In[4]:= constr /. Last[solution] Out[4]= True While maximizing, Mathematica throws some warnings about the impossibilitiy to find startvalues according to the constraints. If it tries r==0 first, the first constraint becomes 0>=l*nfec, which is of course impossible. I would ignore these warnings. HTH Peter