redefine array in for loop

Question

Sara 2012-7-5

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/42827-redefine-array-in-for-loop

Hi Guys,

   for n = 3:length(x)
      y1 = x(2:n) ;
      t1 = ((n-2):-1:0)*dt ;
     % y2 = x(1:n-1) ;
      y2 = y1 - 1 ;
      t2 = t1 +dt; 
      int(n) = sum (t1.^(k-1)/factorial(k-1).*y1 + t2.^(k-1)/factorial(k-1).*y2)*dt/2 ;
end

I want to define y2= y1 -1 instead y2= x (1:n-1) which I have commented above. By y2 = y1 - 1, occurred some errors in MATLAB. Why? It is not correct?

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Walter Roberson 2012-7-6

What error did you encounter with the code you tried?

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Answer 1

John Petersen 2012-7-5

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/42827-redefine-array-in-for-loop#answer_52653

y1-1 means the vector y1 with the quantity 1 subtracted from it. The commented code shifts the elements by one element. Which do you want to do?

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Sara 2012-7-11

在 MATLAB Online 中打开

int = zeros(1,length(x));
if k <= 0
    int = x ;
    return
end
for n = 3:length(x)
      y1 = x(2:n) ;
      t1 = ((n-2):-1:0)*dt ;
     y2 = x(1:n-1) ;
     % y2 = -1 +y1 ;
      t2 = t1 +dt; 
      int(n) = sum (t1.^(k-1)/factorial(k-1).*y1 + t2.^(k-1)/factorial(k-1).*y2)*dt/2 ;
end

I mean, is there anyway to define y2 from y1? And not from variable x? Could I omit the variable y2 from the code ?

F. 2012-7-11

在 MATLAB Online 中打开

If you don't use y1 and y2 after...

   if k <= 0
     int = x ;
     return
   else
     int = zeros(1,numel(x));
   end
   for n = 3:numel(x)
      t1 = ((n-2):-1:0)*dt ;
      t2 = t1 +dt; 
      int(n) = sum ( ...
         t1.^(k-1)/factorial(k-1) .* x( 2 : n   ) + ...
         t2.^(k-1)/factorial(k-1) .* x( 1 : n-1 ) ...
         )*dt/2 ;
   end