Manual implementation of filtfilt(b,a,x) or filter(b,a,x,zi)?

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ssp 2017-2-13

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/324703-manual-implementation-of-filtfilt-b-a-x-or-filter-b-a-x-zi

回答： Jan 2017-2-13

Hi!

I want to implement 'filtfilt' function in C. 'filtfilt' function has 'filter' as its subfunction.

I could implement y=filter(b,a,x) as follows:

y(n) = b(1)*x(n) + b(2)*x(n-1) + ... + b(nb+1)*x(n-nb) - a(2)*y(n-1) - ... - a(na+1)*y(n-na).........equation-1

Now accept the fact that I already have "zi" , how to implement y=filter(b,a,x,zi)? where, Zi=initial condition of the delay. What would be the change in equation-1 after the application of Zi?

Or is there any other way to implement directly filtfilt(b,a,x) in C?

Thanks!

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Answer 1

Jan 2017-2-13

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/324703-manual-implementation-of-filtfilt-b-a-x-or-filter-b-a-x-zi#answer_254527

For an implementation of filter() in C see https://www.mathworks.com/matlabcentral/fileexchange/32261-filterm . Inside FilterM.m you find code for an M-version also. In opposite to Matlab's filter() this C-version can operate in backward direction also to save the time for the creation of a reversed signal in filtfilt().