I keep getting this error:

Question

Gentian Zavalani 2013-6-3

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/77871-i-keep-getting-this-error

clear all
M=input('Enter M =')
N=input('Enter N=')
r=input('Enter r=')
f=input('Enter f=')
L=pi;
h=L/M;
%------&------------------------&------------------------------&-----------------*
%Ne kete program behet zgjidhja numerike e nje problemi diferencial valor
%me shuarje kufitare.Metoda e perdorur eshte ajo e tipit te
%karakteristikave .Ajo shfrytezon rrjetin specifik  te nyjeve qe gjenerojne
%kurbat karakterisitke te ekuacionit si dhe vecorite e kushteve
%fillestare-kufitare te problemit 
%-------&-----------------------&---------------------------------&--------------* 
for i=1:M+1
x(i,1)=i*h;
u(i,1)=sin(x(i,1));
xu(i,1)=cos(x(i,1));  %derivati ne lidhje me x;
tu(i,1)=cos(x(i,1)); %derivati ne lidhje me t;
end
     for j=1:N+1
           for i=2:M
            xu(x(i,j+1))=1/2*[cos(x(i,j))+cos(x(i-1,j))+cos(x(i,j))-cos(x(i-1,j))]+h/8*[r*(cos(x(i,j))-(1/f)*(cos(x(i,j))))-r*(cos(x(i-1,j))-(1/f)*(cos(x(i-1,j))))];
            tu(x(i,j+1))=1/2*[cos(x(i,j))-cos(x(i-1,j))+cos(x(i,j))+cos(x(i-1,j))]+h/8*[r*(cos(x(i,j))-(1/f)*(cos(x(i,j))))+2*(r*(cos(x(i,j+1))-(1/f)*(cos(x(i,j+1)))))+r*(cos(x(i-1,j))-(1/f)*(cos(x(i-1,j))))];
            u(x(i,j+1))=1/2*[sin(x(i-1,j))+sin(x(i,j))]+h/8*[cos(x(i-1,j))-cos(x(i,j))+cos(x(i-1,j))+2*cos(x(i,j+1))+cos(x(i,j))];
           end
     end

------------------------------------------------------------------------------

??? Index exceeds matrix dimensions.
Error in ==> MOC at 30
          xu(x(i,j+1))=1/2*[cos(x(i,j))+cos(x(i-1,j))+cos(x(i,j))-cos(x(i-1,j))]+h/8*[r*(cos(x(i,j))-(1/f)*(cos(x(i,j))))-r*(cos(x(i-1,j))-(1/f)*(cos(x(i-1,j))))];

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Answer 1

Walter Roberson 2013-6-3

2
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/77871-i-keep-getting-this-error#answer_87587

You initialize x(:,1) but you use x(:,j) with j > 1

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Gentian Zavalani 2013-6-4

Could suggest me any solution please

Walter Roberson 2013-6-4

You need to assign values to x(i,j) at some point, but I do not know where would be appropriate. My guess would be that it should be done before the "for j" loop, instead of only initializing x(i,1)

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