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while loop iteration in matlab?

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Mary Jon
Mary Jon 2013-12-4
评论： Mary Jon 2013-12-4
If I am have this code as example
while(A>0.0000001);
statment
.
.
.
end
How can save value of A to each iteration until reach 0.0000001?
I mean there is (A) at first iteration, (A) at second iteration,and so on

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采纳的回答

Walter Roberson
Walter Roberson 2013-12-4
K = 1;
A(K) = .... some initial value ...
while( A(K) >0.0000001)
statment
.
.
.
K = K + 1;
A(K) = new value for A
end

更多回答（2 个）

Jeremy Wurbs
Jeremy Wurbs 2013-12-4
If you know how long you're going to iterate for, something like:
numIter = 10;
A_vec = zeros(numIter,1);
A = 10; cnt = 1;
while(A>0)
A_vec(cnt) = A;
A = A-1;
cnt = cnt+1;
end
If you don't know how long you will iterate for you might not be able to preallocate efficiently (which will greatly slow things down). That said, it is legal to do the following:
A_vec = [];
A = 10;
while(A>0)
A_vec(end+1) = A;
A = A-1;
end
dpb
dpb 2013-12-4
A=[];
iter=0;
while...
iter=iter+1;
A(i)=...;
...
end
NB that if iter grows very large the reallocation every iteration above may begin to noticeably slow down the execution. To minimize this, start by preallocating A and filling. You'll have to check for overflow and reallocate if needed or make the initial size large enough to never be exceeded in which case you can then truncate when done.
N=100;
A=zeros(N,1);
iter=0;
while...
if iter==N, A=[A; zeros(1,N)]; N=N+N; end % add another chunk
iter=iter+1;
A(i)=...;
...
end

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