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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".)

Asked by Riyadh Salim on 11 Nov 2019 at 14:06
Latest activity Edited by James Tursa
on 11 Nov 2019 at 17:11
%task4
function adaptive
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

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What is your question? Where is the error?

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1 Answer

Answer by James Tursa
on 11 Nov 2019 at 17:10
Edited by James Tursa
on 11 Nov 2019 at 17:11

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?

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