Andreas Wittmann <andreas_wittmann <at> gmx.de> writes:
>
> Dear R-users,
>
> i try to solve to following linear programm in R
>
> 0 * x_1 + 2/3 * x_2 + 1/3 * x_3 + 1/3 * x_4 = 0.3
> x_1 + x_2 + x_3 + x_4 = 1
> x_1, x_2, x_3, x_4 > 0,
> x_1, x_2, x_3, x_4 < 1
>
> as you can see i have no objective function here besides that i use the
> following code.
>
> library(lpSolve)
>
> f.obj<-c(1,1,1,1)
> f.con<-matrix(c(0,2/3,1/3,1/3,
> 1,1,1,1,
> 1,0,0,0,
> 0,1,0,0,
> 0,0,1,0,
> 0,0,0,1),nrow=6,byrow=TRUE)
> f.dir <- c("=", "=", ">", ">", ">", ">")
> f.rhs <- c(0.3, 1, 0, 0, 0, 0)
>
> lp ("max", f.obj, f.con, f.dir, f.rhs)$solution
>
> the problem is, the condition x_1, x_2, x_3, x_4 > 0 is not fulfilled.
With strict inequalities x_i > 0 your problem will not have a solution. That is
why in linear programming strict inequalities are replaced with non-strict
inequalities, or as the lp_solve manual says:
"The inequalities can be <=, >= or =
Because all numbers are real values,
<= is the same as < and >= is the same as > ."
Try x_i >= eps > 0 with some eps appropriate for your problem.
Hans Werner
> Any advice would be very helpful.
>
> best regards
>
> Andreas
>
>
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