MATLAB: Global variable in for loop

for loopMATLAB

Hi,

I have a for loop, which has last iterative defined as the size of some matrix K, i.e.

[a,b]=size(K)

for i=1:a

CODE

end

Trouble is, the "CODE" in the for loop redefines how large K is – in particular, it decreases a. This means that the for loop experiences an "Index exceeds matrix dimensions." error. How does one go about fixing this? I thought that in the for loop I could have:

a=a-1;

everytime the "CODE" decreases the size of K, but it don't work none!

Thanks,

Linford

Best Answer

If you are deleting the entry you are examining under some circumstances, then the easiest change is often to run the loop backwards .

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MATLAB: Matrix splitting to overcome “array exceeds maximum array size”

Something like this:

subklength = 100; %whatever you want
transK = K';
for kstart = 1 : subklength : size(k, 1)
  S = N * transK(:, kstart : min(end, kstart+subklength-1))'; %S for section of K
  %do something with S
end

MATLAB: For loops vs. While loops

The FOR loop is nicer and more compact, if the number of iterations is known before the loop is started. The WHILE loop is nicer, when the number of iterations is determined inside the loop.

Compare:

for k = 1:10
  disp(k);
end

with:

k = 1;
while k <= 10
  disp(k);
  k = k + 1;
end

On the other hand:

a = 1e6;
while a > 1
  a = a * rand;
end

with this (1e8 is an arbitrary large guess - a bad idea!):

a = 1e6;
for k = 1:1e8   % Ugly, although it is not created explicitly
  a = a * rand;
  if a <= 1
    break; 
  end
end

There are some overlaps, e.g. running an iteration until a certain number of loops or a specific criterion is reached. Then usually WHILE is preferred with the convergence limit as test, because this reflects the main character of the loop, while the limitation of iterations is a fallback mechanism only.

Best Answer

Related Solutions

MATLAB: Matrix splitting to overcome “array exceeds maximum array size”

MATLAB: For loops vs. While loops

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