-- |
-- Module : Simulation.Aivika.Var
-- Copyright : Copyright (c) 2009-2015, David Sorokin
-- License : BSD3
-- Maintainer : David Sorokin
-- Stability : experimental
-- Tested with: GHC 7.8.3
--
-- This module defines a variable that is bound up with the event queue and
-- that keeps the history of changes storing the values in arrays, which
-- allows using the variable in differential and difference equations of
-- System Dynamics within hybrid discrete-continuous simulation.
--
module Simulation.Aivika.Var
(Var,
varChanged,
varChanged_,
newVar,
readVar,
varMemo,
writeVar,
modifyVar,
freezeVar) where
import Data.Array
import Data.Array.IO.Safe
import Simulation.Aivika.Internal.Specs
import Simulation.Aivika.Internal.Simulation
import Simulation.Aivika.Internal.Dynamics
import Simulation.Aivika.Internal.Event
import Simulation.Aivika.Ref
import Simulation.Aivika.Signal
import qualified Simulation.Aivika.Vector as V
import qualified Simulation.Aivika.Vector.Unboxed as UV
-- | Like the 'Ref' reference but keeps the history of changes in
-- different time points. The 'Var' variable is safe to be used in
-- the hybrid discrete-continuous simulation.
--
-- For example, the memoised values of a variable can be used in
-- the differential or difference equations of System Dynamics, while
-- the variable iself can be updated wihin the discrete event simulation.
--
-- Only this variable is much slower than the reference.
data Var a =
Var { varXS :: UV.Vector Double,
varMS :: V.Vector a,
varYS :: V.Vector a,
varChangedSource :: SignalSource a }
-- | Create a new variable.
newVar :: a -> Simulation (Var a)
newVar a =
Simulation $ \r ->
do xs <- UV.newVector
ms <- V.newVector
ys <- V.newVector
UV.appendVector xs $ spcStartTime $ runSpecs r
V.appendVector ms a
V.appendVector ys a
s <- invokeSimulation r newSignalSource
return Var { varXS = xs,
varMS = ms,
varYS = ms,
varChangedSource = s }
-- | Read the first actual, i.e. memoised, value of a variable for the requested time
-- actuating the current events from the queue if needed.
--
-- This computation can be used in the ordinary differential and
-- difference equations of System Dynamics.
varMemo :: Var a -> Dynamics a
varMemo v =
runEventWith CurrentEventsOrFromPast $
Event $ \p ->
do let xs = varXS v
ms = varMS v
ys = varYS v
t = pointTime p
count <- UV.vectorCount xs
let i = count - 1
x <- UV.readVector xs i
if x < t
then do a <- V.readVector ys i
UV.appendVector xs t
V.appendVector ms a
V.appendVector ys a
return a
else if x == t
then V.readVector ms i
else do i <- UV.vectorBinarySearch xs t
if i >= 0
then V.readVector ms i
else V.readVector ms $ - (i + 1) - 1
-- | Read the recent actual value of a variable for the requested time.
--
-- This computation is destined for using within discrete event simulation.
readVar :: Var a -> Event a
readVar v =
Event $ \p ->
do let xs = varXS v
ys = varYS v
t = pointTime p
count <- UV.vectorCount xs
let i = count - 1
x <- UV.readVector xs i
if x <= t
then V.readVector ys i
else do i <- UV.vectorBinarySearch xs t
if i >= 0
then V.readVector ys i
else V.readVector ys $ - (i + 1) - 1
-- | Write a new value into the variable.
writeVar :: Var a -> a -> Event ()
writeVar v a =
Event $ \p ->
do let xs = varXS v
ms = varMS v
ys = varYS v
t = pointTime p
s = varChangedSource v
count <- UV.vectorCount xs
let i = count - 1
x <- UV.readVector xs i
if t < x
then error "Cannot update the past data: writeVar."
else if t == x
then V.writeVector ys i $! a
else do UV.appendVector xs t
V.appendVector ms $! a
V.appendVector ys $! a
invokeEvent p $ triggerSignal s a
-- | Mutate the contents of the variable.
modifyVar :: Var a -> (a -> a) -> Event ()
modifyVar v f =
Event $ \p ->
do let xs = varXS v
ms = varMS v
ys = varYS v
t = pointTime p
s = varChangedSource v
count <- UV.vectorCount xs
let i = count - 1
x <- UV.readVector xs i
if t < x
then error "Cannot update the past data: modifyVar."
else if t == x
then do a <- V.readVector ys i
let b = f a
V.writeVector ys i $! b
invokeEvent p $ triggerSignal s b
else do a <- V.readVector ys i
let b = f a
UV.appendVector xs t
V.appendVector ms $! b
V.appendVector ys $! b
invokeEvent p $ triggerSignal s b
-- | Freeze the variable and return in arrays the time points and corresponded
-- first and last values when the variable had changed or had been memoised in
-- different time points: (1) the time points are sorted in ascending order;
-- (2) the first and last actual values per each time point are provided.
--
-- If you need to get all changes including those ones that correspond to the same
-- simulation time points then you can use the 'newSignalHistory' function passing
-- in the 'varChanged' signal to it and then call function 'readSignalHistory'.
freezeVar :: Var a -> Event (Array Int Double, Array Int a, Array Int a)
freezeVar v =
Event $ \p ->
do xs <- UV.freezeVector (varXS v)
ms <- V.freezeVector (varMS v)
ys <- V.freezeVector (varYS v)
return (xs, ms, ys)
-- | Return a signal that notifies about every change of the variable state.
varChanged :: Var a -> Signal a
varChanged v = publishSignal (varChangedSource v)
-- | Return a signal that notifies about every change of the variable state.
varChanged_ :: Var a -> Signal ()
varChanged_ v = mapSignal (const ()) $ varChanged v