In the operation of filtfilt, does the filtering process occur in the row direction or the column direction?

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Sho 2023-8-16

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https://ww2.mathworks.cn/matlabcentral/answers/2008972-in-the-operation-of-filtfilt-does-the-filtering-process-occur-in-the-row-direction-or-the-column-di

评论： Sho 2023-8-16

data.mat

I have a question regarding the direction in which filtfilt operates. Time series data is stored for each column, such as in data.mat. I am considering filtering this data separately for each column. My question has two parts:

In the operation of filtfilt, does the filtering process occur in the row direction or the column direction?
If it operates in the row direction, is there a way to make it operate in the column direction?

I appreciate your response.

load data.mat
sampling_rate = 200;
cutoff_frequency = 12;
filter_order = 4;
[b, a] = butter(filter_order, cutoff_frequency / (0.5.*sampling_rate), 'low');
filt_data = [data(:,1:2) filtfilt(b, a, data(:,3:end))]
filt_data = 1049×155
1.0e+03 *

    0.0010         0   -0.3698    1.2958    0.1429   -0.3810    1.2850   -0.1730   -0.3066    0.8857    0.1010   -0.2512    0.8425    0.0766   -0.3297    0.7808    0.1221   -0.2978    0.8054    0.1134   -0.3281    0.6877    0.1396   -0.3339    0.5977    0.1380   -0.3439    0.5118    0.1294   -0.2394
    0.0020    0.0000   -0.3700    1.2958    0.1429   -0.3811    1.2850   -0.1731   -0.3066    0.8856    0.1010   -0.2512    0.8425    0.0766   -0.3297    0.7808    0.1221   -0.2978    0.8054    0.1134   -0.3280    0.6877    0.1397   -0.3339    0.5977    0.1380   -0.3438    0.5118    0.1295   -0.2394
    0.0030    0.0000   -0.3701    1.2959    0.1429   -0.3812    1.2851   -0.1731   -0.3067    0.8856    0.1009   -0.2511    0.8425    0.0766   -0.3297    0.7808    0.1221   -0.2978    0.8054    0.1135   -0.3278    0.6878    0.1397   -0.3339    0.5977    0.1380   -0.3437    0.5118    0.1295   -0.2394
    0.0040    0.0000   -0.3702    1.2959    0.1429   -0.3814    1.2851   -0.1732   -0.3067    0.8856    0.1008   -0.2511    0.8425    0.0766   -0.3297    0.7808    0.1221   -0.2978    0.8054    0.1135   -0.3277    0.6878    0.1397   -0.3339    0.5977    0.1380   -0.3436    0.5117    0.1295   -0.2393
    0.0050    0.0000   -0.3703    1.2959    0.1429   -0.3815    1.2851   -0.1732   -0.3068    0.8856    0.1008   -0.2511    0.8425    0.0766   -0.3296    0.7808    0.1221   -0.2977    0.8054    0.1135   -0.3276    0.6878    0.1397   -0.3338    0.5978    0.1380   -0.3436    0.5117    0.1296   -0.2393
    0.0060    0.0000   -0.3704    1.2959    0.1429   -0.3816    1.2851   -0.1733   -0.3069    0.8856    0.1008   -0.2511    0.8425    0.0766   -0.3296    0.7808    0.1221   -0.2977    0.8054    0.1135   -0.3275    0.6879    0.1398   -0.3338    0.5978    0.1380   -0.3435    0.5117    0.1297   -0.2393
    0.0070    0.0000   -0.3705    1.2959    0.1428   -0.3817    1.2852   -0.1734   -0.3069    0.8856    0.1007   -0.2511    0.8425    0.0766   -0.3296    0.7808    0.1221   -0.2977    0.8054    0.1135   -0.3274    0.6879    0.1398   -0.3338    0.5978    0.1380   -0.3434    0.5117    0.1297   -0.2393
    0.0080    0.0000   -0.3706    1.2959    0.1428   -0.3818    1.2852   -0.1734   -0.3070    0.8856    0.1007   -0.2511    0.8425    0.0766   -0.3296    0.7808    0.1221   -0.2977    0.8054    0.1135   -0.3273    0.6879    0.1398   -0.3337    0.5978    0.1380   -0.3434    0.5117    0.1298   -0.2392
    0.0090    0.0000   -0.3706    1.2959    0.1427   -0.3819    1.2853   -0.1735   -0.3071    0.8856    0.1007   -0.2511    0.8425    0.0766   -0.3296    0.7808    0.1221   -0.2977    0.8054    0.1135   -0.3273    0.6879    0.1398   -0.3337    0.5978    0.1380   -0.3433    0.5117    0.1298   -0.2392
    0.0100    0.0000   -0.3707    1.2959    0.1427   -0.3820    1.2853   -0.1735   -0.3072    0.8856    0.1007   -0.2512    0.8425    0.0765   -0.3296    0.7808    0.1221   -0.2978    0.8054    0.1135   -0.3272    0.6880    0.1398   -0.3336    0.5978    0.1380   -0.3433    0.5117    0.1298   -0.2392

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Answer 1

the cyclist 2023-8-16

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https://ww2.mathworks.cn/matlabcentral/answers/2008972-in-the-operation-of-filtfilt-does-the-filtering-process-occur-in-the-row-direction-or-the-column-di#answer_1287992

编辑：the cyclist 2023-8-16

Per the documentation page filtfilt ...

"The function operates along the first array dimension of x unless x is a row vector. If x is a row vector, then the function operates along the second dimension."

"First array dimension" means down the columns.

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Walter Roberson 2023-8-16

And there is no option to filter along rows when the data is not a row vector. If you need to do that, then transpose, .' or permute before filtfilt and convert back afterwards.

Sho 2023-8-16