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I have a 64*64 block matrix, each block of size 4*4. I need to extract the diagonals of each block as a vector.

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jeje jojo
jeje jojo 2024-1-5
编辑： Matt J 2024-1-5
How to extract the diagonals and print them either one by one or all of them in one vector of 64*^$ block, each block is of size 4*4?
i.e
I have a 256*256 matrix divided into 64*64 blocks, each block is of size 4*4. Now I want to extract only the diagonals of each 4*4 block and print them as a vector.

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Dyuman Joshi
Dyuman Joshi 2024-1-5
编辑：Dyuman Joshi 2024-1-5
Ran in:
You can store them in an array, where each column represent the diagonal of each block.
(I have assumed that the 64*64 blocks are cell elements.)
%Generating random data with a similar structure
%i.e. 64x64 blocks (cell array) with 4x4 block (double array) inside
C = magic(256);
z = 4*ones(1,256/4);
C = mat2cell(C, z, z)
C = 64×64 cell array
Columns 1 through 12 {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} Columns 13 through 24 {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} Columns 25 through 36 {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} Columns 37 through 48 {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} Columns 49 through 60 {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} Columns 61 through 64 {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double} {4×4 double}
out = cellfun(@diag, C, 'uni', 0);
%Using horzcat to get each diagonal as column
OUT1 = horzcat(out{:})
OUT = 4×4096
65536 64512 63488 62464 61440 60416 59392 58368 57344 56320 55296 54272 53248 52224 51200 50176 49152 48128 47104 46080 45056 44032 43008 41984 40960 39936 38912 37888 36864 35840 65279 64255 63231 62207 61183 60159 59135 58111 57087 56063 55039 54015 52991 51967 50943 49919 48895 47871 46847 45823 44799 43775 42751 41727 40703 39679 38655 37631 36607 35583 65022 63998 62974 61950 60926 59902 58878 57854 56830 55806 54782 53758 52734 51710 50686 49662 48638 47614 46590 45566 44542 43518 42494 41470 40446 39422 38398 37374 36350 35326 64765 63741 62717 61693 60669 59645 58621 57597 56573 55549 54525 53501 52477 51453 50429 49405 48381 47357 46333 45309 44285 43261 42237 41213 40189 39165 38141 37117 36093 35069
%For check, compare the diagonal of kth array to the k-column of output
%Here k is 1
C{1}
ans = 4×4
65536 2 3 65533 257 65279 65278 260 513 65023 65022 516 64768 770 771 64765
If you want to print/display them as a vector -
OUT2 = vertcat(out{:})
OUT2 = 16384×1
65536 65279 65022 64765 64512 64255 63998 63741 63488 63231

更多回答（1 个）

Matt J
Matt J 2024-1-5
编辑：Matt J 2024-1-5
A faster method is to use this FEX download,
https://www.mathworks.com/matlabcentral/fileexchange/115340-block-transposition-permutation-and-reshaping-of-arrays
C = magic(256);
A=blkReshape(C,[4,4], 1,1,[]);
out=reshape( A(:,:,1:65:end), 16, [])

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