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Topic: Coding Matlab function "filter" in C++
Replies: 6   Last Post: Feb 11, 2013 11:03 AM

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Peter Boettcher

Posts: 3,594
Registered: 12/4/04
Re: Coding Matlab function "filter" in C++
Posted: Nov 30, 2005 12:54 PM
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"Chris Heier" <> writes:

>> y(n) = k2*x(n) + k1*(1+k2)*x(n-1) + x(n-2) - k1*(1+k2)*y(n-1) - k2*y(n-2)
> Hey thanks. That answers a ton for me. I guess the last thing I had
> on my mind was in regards to n.
> Since X would be a trace containing an array of samples, x[0] would
> contain the first sample. In the algorithm, there is a point where it
> is asking for x[n-1] and x[n-2]. In the case that n would equal 0, the
> first part (n-1) would try to pull a value from the -1 element in the
> array. How would I work around that for the first few elements of the
> array?

Typically the signal is zero-padded. In "help filter", the function
accepts "initial conditions", which would be used instead, in special
applications. Block-based filtering might be one of them, where there
actually are two known values for the input prior to the x[0] in this

Peter Boettcher <>
MIT Lincoln Laboratory

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