How to design aFIR filter without filter function

Question

farhad vaseghi 2020-3-13

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/510674-how-to-design-afir-filter-without-filter-function

评论： farhad vaseghi 2020-3-13

采纳的回答： Sriram Tadavarty

please help me implement this as function to take a,b,x and give me y

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farhad vaseghi 2020-3-13

I wanna impeliment this whith a seprate function

and without,without any use of filter() function!!!!!!!!!!!

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Answer 1

Sriram Tadavarty 2020-3-13

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/510674-how-to-design-afir-filter-without-filter-function#answer_419989

编辑：Sriram Tadavarty 2020-3-13

Hi Farhad,

This code should do what is asked for. Since, you asked for FIR filter, a will be a scalar with value 1.

function y = filterbax(b,a,x)
% The function expects inputs to be column vectors
    M = length(b);
    N = length(a);
    xbuffer = [];
    ybuffer = [];
    for i = 1:length(x)
        xbuffer = [x(i);xbuffer];
        if length(xbuffer) < M
            index = length(xbuffer);
        else
            index = M;
        end
        if length(ybuffer) < N-1
            yindex = length(ybuffer);
        else
            yindex = N-1;
        end
        y(i) = (1/a(1)).*(sum(b(1:index).*xbuffer(1:index)) - sum(a(2:yindex+1).*ybuffer(1:yindex)));
        ybuffer = [y(i);ybuffer];
    end
    y = y(:); % Return as column vector
end

Note that more optimizations can be done, but this should work.

% In command prompt,
% try the following 
>> b = [2,3];
>> a = [1,0.2];
>> x = randn(10000,1);
>> y = filterbax(b,a,x); % Custom function
% Compare the output from custom written function and MATLAB function
>> y1 = filter(b,a,x); % MATLAB function
>> max(abs(y-y1).^2)

Hope this helps.

Regards,

Sriram

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Sriram Tadavarty 2020-3-13

Hi farhad, This is not the same filter function. The name of the function is placed as filterbax which is independent of filter. The bottom code in the answer is just the test with the inbuilt Matlab function. Hope it clears. Regards, Sriram

farhad vaseghi 2020-3-13