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66.67
/MIP/src/Numeric/Optimization/MIP/Solver/Base.hs
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{-# OPTIONS_GHC -Wall #-}
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{-# OPTIONS_HADDOCK show-extensions #-}
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{-# LANGUAGE FunctionalDependencies #-}
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-----------------------------------------------------------------------------
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-- |
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-- Module      :  Numeric.Optimization.MIP.Solver.Base
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-- Copyright   :  (c) Masahiro Sakai 2017
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-- License     :  BSD-style
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--
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-- Maintainer  :  masahiro.sakai@gmail.com
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-- Stability   :  provisional
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-- Portability :  non-portable
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--
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-----------------------------------------------------------------------------
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module Numeric.Optimization.MIP.Solver.Base
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  (
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  -- * Solver type
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    IsSolver (..)
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  , SolveOptions (..)
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  -- * Utilities
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  , Default (..)
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  ) where
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import Data.Default.Class










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import Data.Scientific (Scientific)










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import Numeric.Optimization.MIP.Base as MIP










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import qualified Data.Map as Map










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-- | Options for 'solve' function










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data SolveOptions










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  = SolveOptions










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  { solveTimeLimit :: Maybe Double




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    -- ^ time limit in seconds










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  , solveTol :: Maybe (MIP.Tol Scientific)




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    -- ^ tolerance










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  , solveLogger :: String -> IO ()




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    -- ^ invoked when a solver output a line










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  , solveErrorLogger :: String -> IO ()




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    -- ^ invoked when a solver output a line to stderr










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  , solveCondensedSolution :: Bool




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    -- ^ potentially omit variables set to zero from the solution










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  }










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instance Default SolveOptions where










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  def =




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    SolveOptions




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    { solveTimeLimit = Nothing




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    , solveTol = Nothing




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    , solveLogger = const $ return ()




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    , solveErrorLogger = const $ return ()




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    , solveCondensedSolution = False




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    }










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-- | Type class for solvers










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--










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-- 










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class Monad m => IsSolver s m | s -> m where










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  -- | Low level version of 'solve'' that allows omission of variables with a value 0.










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  --










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  -- Implementor of the type class must implement this method.










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  solve' :: s -> SolveOptions -> MIP.Problem Scientific -> m (MIP.Solution Scientific)










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  -- | A method for solving 'MIP.Problem'










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  --










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  -- This method is a bit higher level than 'solve'' in that it does not omit variables










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  -- with a value @0@ unless 'solveCondensedSolution' is set to @True@.










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  -- Implementor of the type class can override this method as @solve = solve'@ if the










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  -- solver always returns all variables.










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  solve  :: s -> SolveOptions -> MIP.Problem Scientific -> m (MIP.Solution Scientific)










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  solve s opts problem = (if solveCondensedSolution opts then id else addZeroes problem) <$> solve' s opts problem




×







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  {-# MINIMAL solve' #-}










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-- Several solvers (at least CBC) do not include any variables set to 0 in their solution.










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-- TODO: for solvers that do return all variables, add @solve = solve'@










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-- for a minor performance improvement.










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addZeroes :: MIP.Problem Scientific -> MIP.Solution Scientific -> MIP.Solution Scientific










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addZeroes problem (Solution stat obj solmap) = 




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  -- Map.union is left-biased: only values not present in the solution are added.










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  Solution stat obj $ Map.union solmap (Map.fromSet (const 0) (vars problem))




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