Linear indices from colon operator

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Radek
Radek 2024-11-14，15:47
编辑： Stephen23 2024-11-15，8:45
Any array (let's consider only 2D here) can be indexed using colon operator such
array(p1:p2,p3:p4)
How can one generate list of linear indices (for that particular array) from parameters [p1, p2, p3, p4]?

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采纳的回答

Matt J
Matt J 2024-11-14，20:18
[I,J]=ndgrid(p1:p2,p3:p4);
linear=sub2ind(size(array) , I,J);

更多回答（2 个）

Steven Lord
Steven Lord 2024-11-14，15:54
See sub2ind.
  2 个评论
Stephen23
Stephen23 2024-11-14，16:10
编辑：Stephen23 2024-11-15，8:45
Ran in:
Note that in general p1:p2 and p3:p4 when used a indices like that will refer to a rectangular block of that array. So in order to get the linear indices of the entire block you will need to provide SUB2IND with subscript indices for the entire block. One way to achieve this is using NDGRID:
array = randi(9,9,9);
p1 = 3;
p2 = 5;
p3 = 2;
p4 = 5;
[X,Y] = ndgrid(p1:p2,p3:p4);
Z = sub2ind(size(array),X,Y);
array(Z)
ans = 3×4
4 7 2 6 9 9 6 7 1 2 4 8
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array(p1:p2,p3:p4)
ans = 3×4
4 7 2 6 9 9 6 7 1 2 4 8
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Walter Roberson
Walter Roberson 2024-11-14，20:30
Ran in:
@Stephen23
sub2ind() processes the indexes in parallel. All of the indices must be the same size (or else scalars)
sub2ind([4 5],1:2,1:3)
Error using sub2ind (line 61)
Subscript arguments must be scalars or arrays of the same size.

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Catalytic
Catalytic 2024-11-14，20:22
编辑：Catalytic 2024-11-14，20:26
K=createArray(size(array),Fill=sparse(0));
K(p1:p2,p3:p4)=1;
out=find(K); %linear indices
  1 个评论
Matt J
Matt J 2024-11-14，20:33
I would probably do instead,
K=createArray(size(array),Fill=sparse(false));
or maybe just use,
K=false(size(array))
depending on the expected size of the output.

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