Index: mttroot/mtt/bin/trans/p/mtt_update.p
==================================================================
--- mttroot/mtt/bin/trans/p/mtt_update.p
+++ mttroot/mtt/bin/trans/p/mtt_update.p
@@ -1,15 +1,50 @@
 PROCEDURE mtt_update(VAR xnew	: StateVector;
 			 dx,x	: StateVector;
 			 DT	: REAL;
 			 Nx	: INTEGER;
-			 METHOD	: IntegrationMethod);
+			 METHOD	: IntegrationMethod;
+		     VAR A	: StateMatrix);
 
+CONST
+   Small = 0.000001;
+   
 VAR
-i : INTEGER;
+   i,j	 : INTEGER;
+   AA	 : StateMatrix;
+   BB,Ax : StateVector;
+   
+(*$I mtt_solve.p *)
+   
+BEGIN{mtt_update}
+   IF Method=1 THEN {Euler}
+      FOR i := 1 TO  Nx DO
+	 xnew[i] := xnew[i] + dx[i]*DT
+      ELSE IF (Method=2) OR (METHOD=3) THEN {Implicit}
+      BEGIN
+	 {Set up the solution matrices:
+	  AA = eye(Nx)-A*dt
+	  BB = x + dt*(dx - A*x)}
+	 FOR i := 1 TO  Nx DO
+	 BEGIN
+	    Ax[i] := 0.0;
+	    FOR j := 1 TO  Nx DO
+	    BEGIN
+	       AA[i,j] := -A[i,j]*DT;
+	       Ax[i] := Ax[i] + A[i,j]*x[j];
+	       IF i=j THEN
+		  AA[i,j] := AA[i,j] + 1.0;
+	    END
+	 END;
+	 
+	 FOR i := 1 TO  Nx DO
+	    BB[i] := x[i] + DT*(dx[i]-Ax[i]);
+
+	 {Solve the equation AAx = B}
+	 mtt_solve(xnew,AA,BB,Nx,Small);
+      END
+      ELSE
+	 Writeln("Method >2 is not defined");
    
-BEGIN
-   FOR i := 1 TO  Nx DO
-      xnew[i] := xnew[i] + dx[i]*DT;
-END;
+END{mtt_update};