function t=euler1(x0,y0,h,xf)
j=1;
Y(j)=y0;
x(j)=x0;
while (x(j) <= xf)
   j=j+1;
   x(j)=x(j-1)+h;
   Y(j)=Y(j-1)+h*f(x(j-1),Y(j-1));
end
t=Y(j);
