2D Down-sampling matrix

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chrichat
chrichat 2018-3-6
回答： Jongwoo Hong 2020-2-13
Goodevening.
I want to compute a 2D down-sampling matrix (the matrix with which a matrix will be multiplied in order to be downsampled)
d=downsample(eye(initial_size),downsampling_factor);
downs=d(1:downsampling_factor:end,:);
But eye will not work with big number. For example if I want to compute the 170 x 340.000 down-sampling matrix with which a signal of 340.000 x 6 will be multiplied to provide the downsampled 170 x 6 signal.
I have found this alternative but I think is too "naive" with the use of for
d=zeros(1,initial_size);
d(1)=1;
for i=1:sampling_factor
downs(i,:)=circshift(d,[1,sampling_factor*(i-1)]);
end
Thank you in advance.

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回答（1 个）

Jongwoo Hong
Jongwoo Hong 2020-2-13
Hi, I recommend the simple method using transpose.
If you want to downsample M x N matrix A into M/10 x N/5 matrix B (not exact number),
B = transpose(downsample(transpose(downsample(A,10)),5))
will be helpful.

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