If statement in for loop
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I'm trying to add an if statement in my for loop but am not really sure on how to proceed. I am running through iterations with a for loop but would like to change one a value in the calculations if it does not satisfy a certain condition. The code below is for a Runge-Kutta(RK4) scheme, and what I am trying to do is scale my step size h in the (i + 1)th step if the error in the ith step does not satisfy some bound. I have included the code below, and I apologize for how long it is, I am still fairly new to programming and am still pretty inefficient.
h = .01
epsilon = 10^-5
x = 0:h:5
u = zeros(1, length(x));
u(1) = 1;
k1 = zeros(1, length(x));
k2 = zeros(1, length(x));
k3 = zeros(1, length(x));
k4 = zeros(1, length(x));
for i = (1: length(x) - 1)
k1(i) = (5)*u(i);
k2(i) = (5)*(u(i) + (h/2)*k1(i));
k3(i) = (5)*(u(i) + (h/2)*k2(i));
k4(i) = (5)*(u(i) + h*k3(i));
u(i + 1) = u(i) + (h/6)*(k1(i) + 2*k2(i) + 2*k3(i) + k4(i))
err = abs(exp(x(i)) - u(i + 1));
if err > epsilon
h = ((err/epsilon)^(1/5))*h
end
end
plot(x, u)
So basically I want to know how to implement the if statement with in the for loop.
1 comentario
Respuestas (1)
Jan
el 30 de Abr. de 2013
Are you sure you want to calculate exp(i)? It is not likely that the step index matters here. What about exp(x(i))?
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