function RK4=rk4m(f,a,b,ya,h)

%Input    - f is the function 
%            - a and b are the left and right endpoints
%            - ya is the initial condition y(a)
%            - h is the step size
%Output - R = [T' Y'] where T is the vector of abscissas
%              and Y is the vector of ordinates

%If f is an M-file function call R=rk4(@f,a,b,ya,h).
%If f is an anonymous function call R=rk4(f,a,b,ya,h).

M=ceil((b-a)/h);
T=zeros(1,M+1);
Y=zeros(1,M+1);
T=a:h:b;
Y(1)=ya;
for j=1:M
   f1=feval(f,T(j),Y(j));
   f2=feval(f,T(j)+h/2,Y(j)+h*f1/2);
   f3=feval(f,T(j)+h/2,Y(j)+h*f2/2);
   f4=feval(f,T(j)+h,Y(j)+h*f3);
   Y(j+1)=Y(j)+h*(f1+2*f2+2*f3+f4)/6;
end

RK4=[T' Y'];