function proba3
x(1)=0.01;
t(1)=0;
h=0.01;
n=100;
for i=1:n
fx(i)=2*x(i);
if 0.1 < fx(i) & fx(i)< 0.3
    a(i)=0.5
elseif fx(i)<0.1
    a(i)=0.2
else
    a(i)=0
end;
x(i+1)=x(i)+2*h*fx(i);
t(i+1)=t(i)+h;
end;
plot(t,x,'-',t(1:n),fx,'-',t(1:n),a);




function proba3
x(1)=0.01;
t(1)=0;
h=0.1;
n=300;
for i=1:n
fx(i)=sin(x(i));
if 0.1 < fx(i) & fx(i)< 0.3
    h=h
    a(i)=h
elseif fx(i)<0.1
    h=0.5
    a(i)=h
else
    h=0.8*h
    a(i)=h
end;
x(i+1)=x(i)+2*h*fx(i);
t(i+1)=t(i)+h;
end;
plot(t,x,'-',t(1:n),fx,'-',t(1:n),a);