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From: Simon Walter on 5 May 2008 08:12
Hi

I have a signal and I want to identify intervals in which
the signal shows a specific characteristic (that I can
define, e.g. intervals in which the signal is <1). How can I
find such intervals? I want to know the length of each
interval, and how many there are.

Is there anyone who can explain me how to do this?
Thank you!
From: Lorenzo Guerrasio on 5 May 2008 08:41
Let say your signal is S=double 1xN, you can use the sintax:

A=S>1 to create a logical with 0 for values <=1 and 1es for
values >1.
To know how many
values are above 1: sum(A).

To create a vector with only these values:
v=S(S>1)

Hope it helps
"Simon Walter" <saberhagen12(a)yahoo.de> wrote in message
<fvmtmc$k73$1(a)fred.mathworks.com>...
> Hi
>
> I have a signal and I want to identify intervals in which
> the signal shows a specific characteristic (that I can
> define, e.g. intervals in which the signal is <1). How
can I
> find such intervals? I want to know the length of each
> interval, and how many there are.
>
> Is there anyone who can explain me how to do this?
> Thank you!

From: Miroslav Balda on 5 May 2008 08:43
"Simon Walter" <saberhagen12(a)yahoo.de> wrote in message
<fvmtii$dc2$1(a)fred.mathworks.com>...
> Hi
>
> I have a signal and I want to identify intervals in which
> the signal shows a specific characteristic (that I can
> define, e.g. intervals in which the signal is <1). How can I
> find such intervals? I want to know the length of each
> interval, and how many there are.
>
> Is there anyone who can explain me how to do this?
> Thank you!

Hi

The problem may be solved by a logical indexing. If x is a
vector of a signal, then

L=x<1; % is vector of logical values
l = sum(L); % lentgth of the vector x(L), e.g.
% number of values of x fulfilling the condition

Hope it heps.

Mira

From: Jos on 5 May 2008 09:13
"Simon Walter" <saberhagen12(a)yahoo.de> wrote in message
<fvmtii$dc2$1(a)fred.mathworks.com>...
> Hi
>
> I have a signal and I want to identify intervals in which
> the signal shows a specific characteristic (that I can
> define, e.g. intervals in which the signal is <1). How can I
> find such intervals? I want to know the length of each
> interval, and how many there are.
>
> Is there anyone who can explain me how to do this?
> Thank you!

Use logical indexing. If X represents your signal then

Q = X < 1

will give you logical ones where X is smaller than 1. Then
using STRFIND you can get the indices into Q where X starts
and ends being smaller than 1

startind = strfind([0 Q],[0 1]) ;
endind = strfind([Q 0],[1 0]) ;

(ask yourself why you want to pad Q with zero?)

which can be used to get the lengths.

Tip: try this with a small input signal X, for instance:
X = [0 0 2 2 2 0 0 2 2] ;
....

so you can follow the flow.

hth
Jos



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