## can someone help me to solve this error (This statement is not inside any function. (It follows the END that terminates the definition of the function "RK4".)

on 11 Nov 2019
Latest activity Edited by James Tursa

### James Tursa (view profile)

on 11 Nov 2019
close all;
y = [0:0]; T = [0];
h = 0.001;
t = 0; i = 1;
err = 1e-3;
while t < 0.5
e = 1;
%h = 0.01;
while (e > err)
y_1 = y(:,i) + h * f(t, y(:,i));
y_2 = y(:,i) + h/2 * f(t, y(:,i));
y_2 = y_2 + h/2 * f(t+h/2, y_2);
e = 2^1*(norm(y_2 - y_1))/(2^1-1);
if (e > err)
h = 0.9 * h*(err*(2^1-1)/(2^1*(norm(y_2-y_1))));
end
end
y(:,i+1) = y_2;
t = t + h; i = i + 1;
T(i) = t;
if (e < 0.5 * err)
h = h*2;
end
end
end
function euler(i, h, t, ye)
ye(i+1) = ye(i) + h*( f( t(i), ye(i) ) );
end
function impli(i, h, t, y_i)
y_i(i)= yi(i) + h*( f( t(i), yi(i) ) );
yi(i+1)=yi(i) + h*(f(t(i+1),y_i(i)));
end
function Heuns(i, h, t, yh)
yh(i+1) = yh(i)+ h/2 * (f(t(i),yh(i)) + f(t(i+1),(yh(i)+ h*f(t(i),yh(i)))));
end
function RK4(i, h, t, yrk)
k1 = f(t(i), yrk(i));
k2 = f(t(i) + h/2, yrk(i) + h/2*k1);
k3 = f(t(i) + h/2, yrk(i) + h/2*k2);
k4 = f(t(i) + h, yrk(i) + h*k3);
yrk(i+1) = yrk(i) + h/6*(k1 + 2*k2 + 2*k3 + k4);
end
%plot(t,ye, 'b');
%figure;
%plot(t, yi, 'r');
%figure;
%plot(t, yh, 'g');
%figure;
%plot(t, yrk, 'y');
%figure;
plot(t, ye, 'b',t, yi, 'r', t, yh, 'g', t, yrk, 'y',x,Yx);
legend('euler','impli','Heuns','RK4','Real')
%plot(t, ye)
function dy=f(t,y)
d = 10;
dy = -d*(y-(cos(t)));
end

darova

### darova (view profile)

on 11 Nov 2019
What is your question? Where is the error?

### James Tursa (view profile)

on 11 Nov 2019
Edited by James Tursa

### James Tursa (view profile)

on 11 Nov 2019

Looks like your plot( etc ) and legend( etc ) lines are stuck inbetween two functions. Did you intend them to be inside a script that calls all of your functions?