execution time not proportional to array length

Pavel,

Doubling array size quadruples execution time.

I'm not asking for help debugging code; this is something you need to see.

Look at it under the Matlab Profiler.

Jon

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%MP Toolbox timing anomaly: twice the array size takes four times the execution time

clearvars

Fs = mp('48000');

freq = mp('997');

NumSecs = mp('1');  %record duration in seconds

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N = NumSecs*Fs;

disp(['generating ' num2str(double(NumSecs)) '-second D/A signal'])

y1 = zeros(N,1,'mp');

y2 = zeros(N,1,'mp');

cosom = cos(mp('2*pi')*freq/Fs);

tic

for n=2:N  %for loop necessary in production code

   y1(n) = cosom*y1(n-1);  %7.5 seconds in Matlab Profiler, AMD 3995WX CPU Windows 10

   y2(n) = cosom*y2(n-1);  %7.5 seconds in Matlab Profiler, AMD 3995WX CPU Windows 10

end

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%%% DOUBLING number of array elements takes FOUR times the previous execution time %%%

NumSecs = mp('2');  %record duration in seconds

%%%%%%%%%%%%%%%%% EXACT DUPLICATE (cut & paste) of code block above %%%%%%%%%%%%%%%%

N = NumSecs*Fs;

disp(['generating ' num2str(double(NumSecs)) '-second D/A signal'])

y1 = zeros(N,1,'mp');

y2 = zeros(N,1,'mp');

cosom = cos(mp('2*pi')*freq/Fs);

tic

for n=2:N  %for loop necessary in production code

   y1(n) = cosom*y1(n-1);  %37 seconds in Matlab Profiler, AMD 3995WX CPU Windows 10

   y2(n) = cosom*y2(n-1);  %37 seconds in Matlab Profiler, AMD 3995WX CPU Windows 10

end

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