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What does this mean: K12_global(1:3:6,1:3:6)?

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Telex
Telex 2023-12-4
编辑： Image Analyst 2023-12-4
K12 = K12_global(1:3:6,1:3:6)
I don't know how to interpret that indexing in matrices.
  1 个评论
Dyuman Joshi
Dyuman Joshi 2023-12-4
编辑：Dyuman Joshi 2023-12-4
What exactly do you not know how to interpret?
Did you try searching on this forum for similar questions as mentioned in the 1st point of the help section?
Try dissecting the code into parts and see what each part does.

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回答（2 个）

Torsten
Torsten 2023-12-4
Ran in:
Do you see what happens ?
The new matrix K12 is formed of the elements (1,1),(1+3,1),(1,1+3) and (1+3,1+3) of the original matrix K12_global.
K12_global = rand(9)
K12_global = 9×9
0.0194 0.0262 0.2509 0.2650 0.1267 0.3926 0.6566 0.5265 0.6897 0.7206 0.6288 0.2764 0.5182 0.3594 0.8476 0.4010 0.3064 0.1114 0.2628 0.2054 0.4492 0.5123 0.5923 0.5039 0.5320 0.6925 0.4534 0.4825 0.9864 0.0153 0.6897 0.4487 0.9993 0.0325 0.1075 0.2257 0.5787 0.9988 0.9926 0.4080 0.5705 0.6924 0.1036 0.6637 0.5976 0.0143 0.0776 0.9375 0.1070 0.0775 0.7704 0.9926 0.9436 0.0468 0.6609 0.6836 0.3231 0.5390 0.2477 0.8082 0.4072 0.4094 0.8814 0.7498 0.5859 0.3176 0.0981 0.0715 0.2600 0.2737 0.4692 0.8073 0.4474 0.8309 0.9656 0.1444 0.9107 0.9487 0.6329 0.2216 0.2917
K12 = K12_global(1:3:6,1:3:6)
K12 = 2×2
0.0194 0.2650 0.4825 0.6897
Image Analyst
Image Analyst 2023-12-4
Ran in:
Another example
indexes = 1 : 3 : 6
indexes = 1×2
1 4
The next index would be 7 since 4 + 3 = 7, but since it was told to stop at 6, the 7 does not get included.
K12_global = reshape(1:49, 7, 7)
K12_global = 7×7
1 8 15 22 29 36 43 2 9 16 23 30 37 44 3 10 17 24 31 38 45 4 11 18 25 32 39 46 5 12 19 26 33 40 47 6 13 20 27 34 41 48 7 14 21 28 35 42 49
K12 = K12_global(1:3:6,1:3:6)
K12 = 2×2
1 22 4 25
Basically you can see it gets the intersection of the row indexes (1 & 4) with the column indexes (1 & 4).

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