while loop iteration in matlab?

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

Answer 1

[Walter Roberson]

K = 1;
A(K) = .... some initial value ...

while( A(K) >0.0000001)
  statment
  .
  .
  .
  K = K + 1;
  A(K) = new value for A
end

[Mary Jon]

How can I know the time taken by A to reach convergence in seconds

[dpb]

doc tic % toc

[Mary Jon]

Thank you dpb

Answer 2

[Jeremy Wurbs]

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

Answer 3

[dpb]

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