controllability.hs

module Main where

import Control.Monad (liftM)
import Numeric.LinearAlgebra (readMatrix, multiply, rank, cols, rows, fromBlocks)

main = do
    putStrLn "Enter matrix A (in format \"1 2 3; 4 5 6; 7 8 9\")"
    a <- getMatrix

    putStrLn "Enter matrix B (in format \"1; 2; 3\")"
    b <- getMatrix

    let cm = controllability a b
        c  = isControllable cm

    putStr "Controllability matrix: "
    print cm
    putStr "Is system controllable: "
    print (if c then "yes" else "no")

-- For controllability, every row must be linearly independent.
isControllable cm = rank cm == rows cm 

-- Controllability matrix. See:
-- http://en.wikipedia.org/wiki/Controllability
controllability a b = let
    cm' = iterate (multiply a) b -- Infinite list [b ab aab ...]
    cm  = take (cols a) cm'      -- Finite list of length (cols a)
    in fromBlocks [cm]           -- Glue columns into square matrix

-- Convenience: read matrix using ';' instead of '\n' to separate rows.
getMatrix = liftM lineToMat getLine
   where lineToMat   = readMatrix . map translate
         translate c = if c == ';' then '\n' else c