how can i store a value of a calculation in a loop

Question

Ketan Bharucha 2017-10-5

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评论： jean claude 2017-10-8

Hi I have the following loop.

for k=1:length(hplid)
x=hplid(k);
q=sort(latency(hpl==x));
size(q);
figure;
plot(q,(1:numel(q))/numel(q))
title(['HPL ', num2str(x), ' Latency']);
xlabel('Seconds');
ylabel('% Percentile');
quant=interp1((1:numel(q))/numel(q),q,[.9 .95 .99]);
disp( '90%, 95% and 99% latency');
disp(quant); 
end

how can I store the value of quants to an array everytime the loop is exectued. Right quants only store the calculation of the last iteration of the loop.

Thank you

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Jan 2017-10-5

I have formatted your code using the "{} Code" button.

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Answer 1

Jan 2017-10-5

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https://ww2.mathworks.cn/matlabcentral/answers/359893-how-can-i-store-a-value-of-a-calculation-in-a-loop#answer_284471

编辑：Jan 2017-10-5

在 MATLAB Online 中打开

Store the vectors in a matrix using the loop counter as index:

quant = zeros(length(hplid), 3);  % Pre-allocate!!!
for k = 1:length(hplid)
   ...
   quant(k, :) = interp1((1:numel(q))/numel(q),q,[.9 .95 .99]);
   disp(quant(k, :)); 
end

Note: The line "size(q);" is useless.

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Ketan Bharucha 2017-10-5

I get the following error when I use your solution? any idea?

The following error occurred converting from duration to double: Undefined function 'double' for input arguments of type 'duration'. To convert from durations to numeric, use the SECONDS, MINUTES, HOURS, DAYS, or YEARS functions.

Jan 2017-10-6

@Ketan: Please post the complete error message and the relevant part of the code. I can neither guess, which line causes the error, nor which variable has the type "duration". Note that the message contains a hint about the solution already.

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Answer 2

jean claude 2017-10-5

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https://ww2.mathworks.cn/matlabcentral/answers/359893-how-can-i-store-a-value-of-a-calculation-in-a-loop#answer_284473

在 MATLAB Online 中打开

try this put it just before end of the loop

quantvalue=[];
quantvalue=[quantvalue quant];

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Walter Roberson 2017-10-5

This works, but is not efficient. Each time something is added on to the end of quantvalue, MATLAB has to look for new memory long enough to store the combined results, and copy the existing quantvalue over and then copy in the new values, and then throw away the existing quantvalue. When possible, it is much more efficient to allocate the memory to store all of the results and write them in as you go.

jean claude 2017-10-8