redefine array in for loop

2012 7 5
1 个回答
2 次查看（30 天）

0 个投票

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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回答（1 个）

John Petersen
John Petersen 2012-7-5

0 个投票

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?

5 个评论
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Sara
Sara 2012-7-5
I intend instead of defining the variable y2 with x(1:n-1) , define it by y1 -1 . Maybe I can omit the y2 variable.
F.
F. 2012-7-5
could you give us an exemple of x ??? I'm ok with John y2 = x(1:n-1) and y2 = y1 - 1 , it's not the same thing !!!
John Petersen
John Petersen 2012-7-5
I think you want to shift the elements by 1, but you want to define it your own way. If you want to use Matlab, you need to use it's syntax.
Sara
Sara 2012-7-11
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.
F. 2012-7-11
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

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Sara
Sara
2012-7-5

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