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This library implements a simple eDSL for linear programming and a simple
wrapper around lp_solve (potentially other solvers can also be plugged in
easily). Here's how to solve the farmer example from the lp_solve
documentation:
> Suppose a farmer has 75 acres on which to plant two crops: wheat and barley.
> To produce these crops, it costs the farmer (for seed, fertilizer, etc.) $120
> per acre for the wheat and $210 per acre for the barley. The farmer has
> $15000 available for expenses. But after the harvest, the farmer must store
> the crops while awaiting favourable market conditions. The farmer has storage
> space for 4000 bushels. Each acre yields an average of 110 bushels of wheat
> or 30 bushels of barley. If the net profit per bushel of wheat (after all
> expenses have been subtracted) is $1.30 and for barley is $2.00, how should
> the farmer plant the 75 acres to maximize profit?
import Control.Monad
import Math.LinProg.LPSolve
import Math.LinProg.Types
data Crop = Wheat | Barley
deriving (Eq, Show, Ord)
lp :: LinProg Double Crop ()
lp = do
let vs@[w, b] = map var [Wheat, Barley]
obj $ negate $ 110 * 1.3 * w + 30 * 2 * b
120 * w + 210 * b <: 15000
110 * w + 30 * b <: 4000
w + b <: 75
main :: IO ()
main = do
sol <- solve lp
print sol
This outputs the solution: Right [(Wheat,21.875),(Barley,53.12499999999999)].
Due to the monadic structure one can build up LPs using the usual monadic
controls such as mapM/forM etc, making it quite easy to specify constraints.
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