function [f]=fvinc(t,y)
[n,m]=size(y); f=zeros(n,m);
phix='2*y(1)';
phiy='2*y(2)';
phiz='2*y(3)';
H=2*eye(3);
mass=1;  % Mass
F1='0*y(1)';
F2='0*y(2)';
F3='-mass*9.8'; % Weight
xdot=zeros(3,1);
xdot(1:3)=y(4:6);
F=[eval(F1);eval(F2);eval(F3)];
G=[eval(phix);eval(phiy);eval(phiz)];
lambda=(mass*xdot'*H*xdot+F'*G)/(G'*G);
f(1:3)=y(4:6);
for k=1:3;
  f(k+3)=(F(k)-lambda*G(k))/mass;
end
return
