Index exceeds the number of array elements (2) Error

Question

Joshua Steil 2019-3-13

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https://ww2.mathworks.cn/matlabcentral/answers/449954-index-exceeds-the-number-of-array-elements-2-error

评论： Brian Hart 2019-3-13

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Receiving the following error after running this code...

Index exceeds the number of array elements (2).

Error in Temp1 (line 23)

h(i) = -1 * (it(i) + vt(i)/Rleq);

deltat = .1/1000;
Tmax = 10/1000;
R = 10;
L = 20*10^-3;
V = 10;
I0 = 0;
CDA = input('Input: ');
it(1) = I0;
vt(1) = 0;
Rleq = 2*L/deltat;
Isrc = V/R;
Kmax = Tmax/deltat;
for i = 2:Kmax+1
    if (i==2)&&(CDA==0)
        h(i-1) = -1 * it(1);
        vtemp = (Isrc + h(i-1))/(1/R + 1/Rleq);
        itemp = vtemp/Rleq - h(i-1);
        h(i) = -1 * itemp;
        vt(i) = (Isrc + h(i))/(1/R + 1/Rleq);
        it(i) = vt(i)/Rleq - h(i);
    else
h(i) = -1 * (it(i) + vt(i)/Rleq);
vt(i) = (Isrc + h(i))/(1/R + 1/Rleq);
it(i) = vt(i)/Rleq - h(i);
    end
end

Any help getting this code to work would be greatly appreciated!

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Brian Hart 2019-3-13

Well, it and vt are variables with one element, then your for-loop starts at 2, and tries to access the second element (looking at line 22, it(i) will be it(2) on the first iteration). That's why the "Index exceeds the number of array elements"

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Answer 1

Geoff Hayes 2019-3-13

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Joshua - the line of code

h(i) = -1 * (it(i) + vt(i)/Rleq);

is trying to access the third (for case i is 3) the third element of it and vt...but these have not yet been set. I suspect that you may want to do

h(i) = -1 * (it(i-1) + vt(i-1)/Rleq);

and then on the next two lines we update these two arrays as

vt(i) = (Isrc + h(i))/(1/R + 1/Rleq);
it(i) = vt(i)/Rleq - h(i);

Note that this works fine so long as the input parameter is 0 because of

if (i==2)&&(CDA==0)

If CDA is not zero then the above will never evaluate to true and you will have the same indexing problem as before.

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Answer 2

Walter Roberson 2019-3-13

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Your assignment to h(i) after the if expects vt(i) to have been assigned to. However, if the if condition was false, then the assignment statements will have been skipped, leaving vt(i) undefined.

Unfortunately you cannot just exchange the assignments to h(i) and vt(i) because vt(i) needs h(i) to have been defined

Perhaps you should be referring to vt(i-1)