added options and hookified kernel

Author: mahrud

M2/Macaulay2/m2/matrix1.m2

@@ -578,6 +578,28 @@ Ideal ^ Array := (I, e) -> (
    ideal phi generators I
 )
 
+-----------------------------------------------------------------------------
+-- kernel and homology
+-----------------------------------------------------------------------------
+
+kernel = method(Options => {
+	DegreeLimit  => {},
+	Strategy     => {},
+	SubringLimit => infinity, -- stop after finding enough elements of a subring
+    })
+kernel Matrix := Module => opts -> g -> g.cache.kernel ??= if g == 0 then source g else tryHooks(
+    (kernel, Matrix), (opts, g), (opts, g) -> (
+	-- this is the default algorithm
+	-- compare with homology below
+	N := source g;
+	P := target g;
+	g = matrix g;
+	if P.?generators then g = P.generators * g;
+	h := modulo(g, if P.?relations then P.relations);
+	if N.?generators then h = N.generators * h;
+	subquotient(h, if N.?relations then N.relations)))
+kernel RingElement := Module => opts -> f -> kernel(matrix {{f}}, opts)
+
 homology(Matrix,Matrix) := Module => opts -> (g,f) -> (
      if g == 0 then cokernel f
      else if f == 0 then kernel g

M2/Macaulay2/m2/pushforward.m2

@@ -227,22 +227,13 @@ scan({Default, Quotient}, strategy ->
 -- kernel
 -----------------------------------------------------------------------------
 
-kernel Matrix := Module => opts -> (cacheValue symbol kernel) ((m) -> (
-	  N := source m;
-	  if m == 0 then return N;
-	  P := target m;
-	  if m.?RingMap then (
-	       f := m.RingMap;
-	       n := map(target m,f source m,raw m);
-	       p := pushNonLinear(options pushForward, f, coimage n);
-	       image p)
-	  else (
-	       m = matrix m;
-	       if P.?generators then m = P.generators * m;
-	       h := modulo(m, if P.?relations then P.relations);
-	       if N.?generators then h = N.generators * h;
-	       subquotient( h, if N.?relations then N.relations))))
-kernel RingElement := Module => options -> (m) -> kernel (matrix {{m}},options)
+addHook((kernel, Matrix), Strategy => "PushForward",
+    (opts, m) -> if m.?RingMap then (
+	N := source m;
+	P := target m;
+	f := m.RingMap;
+	M := coimage map(target m, f ** source m, raw m);
+	image pushNonLinear(options pushForward, f, M)))
 
 -- Local Variables:
 -- compile-command: "make -C $M2BUILDDIR/Macaulay2/m2 "

M2/Macaulay2/m2/ringmap.m2

@@ -228,7 +228,6 @@ RingMap \ VisibleList := VisibleList => (f,v) -> apply(v,x -> f x)
 -- kernel
 -----------------------------------------------------------------------------
 
-kernel = method(Options => { SubringLimit => infinity })
 kernel RingMap := Ideal => opts -> (cacheValue (symbol kernel => opts)) (f -> (
     (F, R) := (target f, source f);
     if 0_F == 1_F then return ideal 1_R;

M2/Macaulay2/packages/Macaulay2Doc/functions/kernel-doc.m2

@@ -3,6 +3,11 @@
 --- author(s): 
 --- notes: 
 
+undocumented {
+    [kernel, DegreeLimit],
+    [kernel, Strategy],
+}
+
 doc ///
 Node
   Key