Help with knowing what kind of vector im using

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Lavorizia Vaughn 2021-11-13

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https://ww2.mathworks.cn/matlabcentral/answers/1585594-help-with-knowing-what-kind-of-vector-im-using

评论： Lavorizia Vaughn 2021-11-13

could someone tell me what th2s=[th2s,y(2)] means?

th1=1;
th2=1;
w1=0;
w2=0;
hs(1)=[0.05];
hs(2)=[0.05/2];
hs(3)=[0.05/4];
hs(4)=[0.05/8];
hs(5)=[1/1000];
th2s=[];
for h=hs %for all the stepsizes
    y=[th1,th2,w1,w2]; we have this vetir which has the values
    N=100/h;
    for i=1:N
        k1= h*fpend(y);
        k2=h*fpend(y + k1/2);
        k3=h*fpend(y + k2/2);
        k4= h*fpend(y + k3);
        y = y + (k1 + 2*k2 + 2*k3 + k4) / 6;
    end
    th2s=[th2s,y(2)]
end

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Answer 1

Cris LaPierre 2021-11-13

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It is appending y(2) to the end of the vector th2s at the end of each h loop.

th2s=[];
for a=1:3
    a
    th2s = [th2s,a]
end
a = 1
th2s = 1
a = 2
th2s = 1×2
     1     2
a = 3
th2s = 1×3
     1     2     3

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Cris LaPierre 2021-11-13

It looks like you are doing a 4th order runge-kutta. There are a lot of questions about implementing that on Answers. Take a look at some of them for ideas. Your code looks pretty clean. Just be sure to place a % before any comments.

Lavorizia Vaughn 2021-11-13