Диференциални уравнения

Рунге-Кута от четвърти ред

a=0;
b=0.5;
h=0.1;
y=1;
x=a;
n=((b-a)/h);
f[x_,y_]:=0.2*y;
yt[x_]:=Exp[0.2x]
points={{,}};
For[i=0, i≤n,i++,
err=Abs[y-yt[x]];
Print["i= ", i, " x= ",x," y= ",y, " f(x,y)= ", f[x,y], " yt = ", yt[x], " error= ",err];
k1=h*f[x,y];
k2=h*f[x+(h/2),y+(k1/2)];
k3=h*f[x+(h/2),y+(k2/2)];
k4=h*f[x+h,y+k3];
AppendTo[points,{x,y}];
y=y+(1/6)(k1+2k2+2k3+k4);
x=x+h
]
Print[points];
grfP=ListPlot[points,PlotStyle->PointSize[0.04]];
grfY=Plot[yt[x],{x,0,5},PlotStyle->Red];
Show[grfP,grfY]