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Re: question about maximization with mathematica tool

  • To: mathgroup at smc.vnet.net
  • Subject: [mg109412] Re: question about maximization with mathematica tool
  • From: Bob Hanlon <hanlonr at cox.net>
  • Date: Mon, 26 Apr 2010 04:50:17 -0400 (EDT)

You need to include at least the lower boundary for x

expr = FullSimplify[Rationalize[
    12 La*T + (0.12 x + 5 y)*((2 (42 x + 4018 y - 7 x y))/
         (9 x y) - (6 x + 574 y - x*y)^2/(2025 x^2 y^2))]];

(Maximize[{expr /. y -> 7/2, 80 <= x < 250}, x] //
   Simplify) /. 
 r_Rational :> N[r]

{12 La T+331.744,{x->80}}

(Maximize[{expr /. y -> 2, 80 <= x < 250}, x] //
   Simplify) /. 
 r_Rational :> N[r]

{12 La T+278.921,{x->80}}

(Simplify[
   Maximize[{expr,
     80 <= x < 250, y == 7/2 || y == 2}, x],
   y == 7/2 || y == 2]) /. r_Rational :> N[r]

{Piecewise[
     {{12*La*T + 278.9207702469136, 
         y == 2}}, 12*La*T + 
       331.74427087994457], {x -> 80}}


Bob Hanlon

---- MANOLIS <voskakis86 at gmail.com> wrote: 

=============
i want to maximize the equation below:

12La*T + (0.12x + 5 y)*((2 (42 x + 4018 y - 7 x y))/(
    9 x y) - (6 x + 574 y - x y)^2/(2025 x^2 y^2))

it has 4 variables x, y, La, T. I want the maximization for the x
variable only. In other words i want to find a relation between x and
the other variables that maximizes the whole equation. the
restrictions are that 80<x<250 and y==3.5 || y==2

i wrote the command below  in mathematica but nothing:


Maximize[{12La*T + (0.12x + 5y)*((2 (42 x + 4018 y - 7 x y))/(
      9xy) - (6x + 574y - x*y)^2/(2025 x^2 y^2)),
  x < 250 && x > 80, y == 3.5 || y == 2}, {x}]


i dont know why. i dont think that it is the number of variables that
causes the problem...

thank you very much
Manolis



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