How to use "while loop" in this case?

Question

Armando MAROZZI 2021-5-20

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/834928-how-to-use-while-loop-in-this-case

回答： Scott MacKenzie 2021-5-20

采纳的回答： Sulaymon Eshkabilov

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I would like to write a loop that says: "when the number of lags is smaller than the sample size stop it".

This is what I tried:

% N.B. MidasQuantile() is from MIDAS Toolbox
% Random data
y_m = rand(300,1);
% Estimation and forecast
lags = [1:250];
estParams_m = nan(size(lags,2),9);
% Training Sample
while lags(end) < 180
    for j =1:length(tau)
        if j==1
            [estParams_m(lags(end),1:3)] = MidasQuantile(y_m(1:180,:), Quantile',tau(j),'Period',22, 'NumLags', lags(end));
        elseif j==2
            [estParams_m(lags(end),4:6)] = MidasQuantile(y_m(1:180,:),'Quantile',tau(j),'Period',22, 'NumLags', lags(end));
        elseif j==3
             [estParams_m(lags(end),7:9)] = MidasQuantile(y_m(1:180,:),'Quantile',tau(j),'Period',22, 'NumLags', lags(end));           
      end
  end
end

Yet, I get no results with this. Basically, I want the loop to run until the number of lags does not exceed the restricted sample size.

Can anyone help me with this?

Thanks!

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Stephen23 2021-5-20

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lags = [1:250]; % the square brackets are superfluous. Get rid of them.
..
while lags(end) < 180

lags(end) is 250, which is clearly greater than 180. So your WHILE loop does not even get to run one iteration.

Inside the WHILE loop you do not change lags, so even if it did iterate, your code does not change the condition.

Armando MAROZZI 2021-5-20

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thanks for this. So, would this sort the issue?

while lags(1:end) < 180
....
end

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Answer 1

Sulaymon Eshkabilov 2021-5-20

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https://ww2.mathworks.cn/matlabcentral/answers/834928-how-to-use-while-loop-in-this-case#answer_704158

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k=1;
while k < 180
    for ..
    ...
    end
        k=k+1;
end

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Armando MAROZZI 2021-5-20

thanks a lot! Very helpful

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Answer 2

Scott MacKenzie 2021-5-20

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You've got a for-loop inside a while-loop. This is likely unnescessary. Here's approximately what you need...

sampleSize = 180;  % or whatever the sample size is, as per your question
for i=1:length(tau)
    
   % do something that iterates through tau
   
   if i == sampleSize
        break; % exit the loop when you have reached the sample size
   end
end

You can also set this up like this...

sampleSize = 180; % or whatever the sample size is, as per your question
i = 1;
while true
    % do something (using i as index into tau, increment i afterward)
    
    if i > samplesize
        break; % exit the loop when you have reached the sample size
    end
end