2 files changed, 59 insertions, 6 deletions

diff --git a/packages/base/CHANGELOG b/packages/base/CHANGELOG
index 260676f..01aa0fb 100644
--- a/packages/base/CHANGELOG
+++ b/packages/base/CHANGELOG
@@ -40,7 +40,7 @@
 
     * Improved "build", "konst", "linspace", "LSDiv", loadMatrix', and other small changes.
 
-    * Added L1 linear system solver in hmatrix-glpk
+    * In hmatrix-glpk: (:=>:) change to (:>=:). Added L_1 linear system solvers.
 
     * Improved error messages.
 
diff --git a/packages/glpk/src/Numeric/LinearProgramming/L1.hs b/packages/glpk/src/Numeric/LinearProgramming/L1.hs
index 2e8f94a..f55c721 100644
--- a/packages/glpk/src/Numeric/LinearProgramming/L1.hs
+++ b/packages/glpk/src/Numeric/LinearProgramming/L1.hs
@@ -9,6 +9,7 @@ Linear system solvers in the L_1 norm using linear programming.
 -----------------------------------------------------------------------------
 
 module Numeric.LinearProgramming.L1 (
+    l1Solve, l1SolveGT,
     l1SolveO, lInfSolveO,
     l1SolveU,
 ) where
@@ -16,9 +17,9 @@ module Numeric.LinearProgramming.L1 (
 import Numeric.LinearAlgebra
 import Numeric.LinearProgramming
 
--- | L_Inf solution of overconstrained system Ax=b.
+-- | L_inf solution of overconstrained system Ax=b.
 --
--- Find argmin x ||Ax-b||_inf
+-- @argmin_x ||Ax-b||_inf@
 lInfSolveO :: Matrix Double -> Vector Double -> Vector Double
 lInfSolveO a b = fromList (take n x)
   where
@@ -31,10 +32,11 @@ lInfSolveO a b = fromList (take n x)
     p = Sparse (c1++c2)
     Optimal (_j,x) = simplex (Minimize (replicate n 0 ++ [1])) p (map Free [1..(n+1)])
 
+--------------------------------------------------------------------------------
 
 -- | L_1 solution of overconstrained system Ax=b.
 --
--- Find argmin x ||Ax-b||_1.
+-- @argmin_x ||Ax-b||_1@
 l1SolveO :: Matrix Double -> Vector Double -> Vector Double
 l1SolveO a b = fromList (take n x)
   where
@@ -49,11 +51,11 @@ l1SolveO a b = fromList (take n x)
     p = Sparse (c1++c2)
     Optimal (_j,x) = simplex (Minimize (replicate n 0 ++ replicate m 1)) p (map Free [1..(n+m)])
 
-
+--------------------------------------------------------------------------------
 
 -- | L1 solution of underconstrained linear system Ax=b.
 --
--- Find argmin x ||x||_1 such that Ax=b.
+-- @argmin_x ||x||_1 such that Ax=b@
 l1SolveU :: Matrix Double -> Vector Double -> Vector Double
 l1SolveU a y = fromList (take n x)
   where
@@ -65,3 +67,54 @@ l1SolveU a y = fromList (take n x)
     p = Sparse (c1 ++ c2 ++ c3)
     Optimal (_j,x) = simplex (Minimize (replicate n 0 ++ replicate n 1)) p (map Free [1..(2*n)])
 
+--------------------------------------------------------------------------------
+-- | Solution in the L_1 norm, with L_1 regularization, of a linear system @Ax=b@.
+--
+-- @argmin_x  λ||x||_1 + ||Ax-b||_1@
+l1Solve
+    :: Double        -- ^ λ
+    -> Matrix Double -- ^ A
+    -> Vector Double -- ^ b
+    -> Vector Double -- ^ x
+l1Solve λ a b = fromList (take n x)
+  where
+    n = cols a
+    m = rows a
+    as = toRows a
+    bs = toList b
+    c1Res = zipWith3 (mkR (1)) as bs [1..m]
+    c2Res = zipWith3 (mkR (-1)) as bs [1..m]
+    mkR sign a_i b_i k = (zipWith (#) (toList (scale sign a_i)) [1..] ++ [-1#(k+2*n)]) :<=: (sign * b_i)
+    c1Sol = map (\k ->  [ 1#k, -1#k+n] :<=: 0) [1..n]
+    c2Sol = map (\k ->  [-1#k, -1#k+n] :<=: 0) [1..n]
+    p = Sparse (c1Res++c2Res++c1Sol++c2Sol)
+    cost = replicate n 0 ++ replicate n λ ++ replicate m 1
+    Optimal (_j,x) = simplex (Minimize cost) p (map Free [1..(2*n+m)])
+
+--------------------------------------------------------------------------------
+
+-- | Solution in the L_1 norm, with L_1 regularization, of a system of linear inequalities @Ax>=b@.
+--
+-- @argmin_x  λ||x||_1 + ||step(b-Ax)||_1@
+l1SolveGT
+    :: Double        -- ^ λ
+    -> Matrix Double -- ^ A
+    -> Vector Double -- ^ b
+    -> Vector Double -- ^ x
+l1SolveGT λ a b = fromList (take n x)
+  where
+    n = cols a
+    m = rows a
+    as = toRows a
+    bs = toList b
+    cRes = zipWith3 mkR as bs [1..m]
+    mkR a_i b_i k = (zipWith (#) (toList a_i) [1..] ++ [1#(k+2*n)]) :>=: (b_i)
+    c1Sol = map (\k ->  [ 1#k, -1#k+n] :<=: 0) [1..n]
+    c2Sol = map (\k ->  [-1#k, -1#k+n] :<=: 0) [1..n]
+    p = Sparse (cRes++c1Sol++c2Sol)
+    cost = replicate n 0 ++ replicate n λ ++ replicate m 1
+    Optimal (_j,x) = simplex (Minimize cost) p (map Free [1..(2*n)])
+
+--------------------------------------------------------------------------------
+
+