function phi = initpos(x,b,a)
L=length(x);
phi=zeros(1,L);
% for i=1:L
%     if (abs(x(i))>a) 
%         phi(i)=0;
%    else
%         phi(i)=b-b.*abs(x(i))/a;
%     end
% end
for i=1:L
   if (abs(x(i))>a)
       phi(i)=0;
    else
       phi(i)=-3*sin(5*x(i));
   end
end