Counter goes up than down to 1 in recursive function
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Hello,
I want my function to return how many 'moving windows' of a particular size can fit in a given length_n-long signal, with a given hop size.
here is my function :
| function N_n = numWindows( N_n, currentSample_n, hopSize_n, length_n, width_n )
% check if we have reached the end of the signal
if currentSample_n + width_n >= length_n
return
else
currentSample_n = currentSample_n + hopSize_n ;
N_n = N_n + 1;
% here we call the same function on the rest of the signal
numWindows( N_n, currentSample_n, hopSize_n, length_n, width_n );
end
return
end|
This code returns systematically N_n = 2; When I entered debug mode I saw that N_n was increasing normally to the correct value, then as the function exited the "if"s one after the other, I saw that N_n was decreasing 1 by 1, just as it had increased in the first place. And the function stopped with N_n = 2.
I tried it with a while loop but it was quickly taking a very long time as the signals started to get long (= big length_n input value).
I would be very grateful to any kind of advice on this problem, thank you very much !
Léo.
4 个评论
Léonard Roussel
2012-7-4
编辑：Léonard Roussel
2012-7-4
AC
2012-7-4
Nevermind, got it, see answer below.
Léonard Roussel
2012-7-4
采纳的回答
AC
2012-7-4
Ok, I think I got it: I believe you need to recursively output N_n when you are calling numWindows within the function.
I don't know signal processing, so sorry if it doesn't make sense, but if you try:
N_n=numWindows(1,1,2,100,4);
Then you'll get N_n=49 after modification.
Does it sound about right?
4 个评论
AC
2012-7-4
The reason for that, btw, is that in the current form of your function, you only call the "if" once per recursion. So within the recursion it computes all the right things but when you output N_n, you actually only output N_n=2 which corresponds to the first recursion. By the way, if you output currentSample_n as well, you'll have the same problem. So to make things very clear, here's how you may want to change your function:
function [N_n currentSample_n] = numWindows( N_n, currentSample_n, hopSize_n, length_n, width_n )
% check if we have reached the end of the signal
if currentSample_n + width_n >= length_n
return
else
currentSample_n = currentSample_n + hopSize_n ;
N_n = N_n + 1;
% here we call the same function on the rest of the signal
[N_n currentSample_n]=numWindows( N_n, currentSample_n, hopSize_n, length_n, width_n );
end
AC
2012-7-4
You should then get:
[N_n c]=numWindows(1,1,2,100,4)
N_n =
49
c =
97
Léonard Roussel
2012-7-4
AC
2012-7-4
Sure :) What changes is just the storage of your variable, not the computations. When you compute N_n=N_n+1; you do it within the recursive function (except for the first one), but you never actually store it. It's quite tricky, a bit like time travel :)
更多回答（1 个）
Léonard Roussel
2012-7-4
0 个投票
1 个评论
AC
2012-7-4
Did you try the bit of code I just submitted? It works on my computer. (I think we posted at the same time :))
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