Four indexing matrix

I have a matrix nxn, each element is described by a 2 index number (i.e. one number for the column, one for the row). The problem is that i want to access this matrix by a four digit indexing. Is there a way to do that?

[Oleg Komarov]

What do you mean? You want to retrieve two points at the same time?

[Nikolaos]

no, i want to access a matrix not by 2 digits indexing but by 4 index indexing. For example i want to map A(k,l,m,n)->p(i,j) {where i==row, j=column of p matrix }

[Jan]

There is an infinite number of possibilities to map "A(k,l,m,n)->p(i,j)". Please specify how {k,l,m,n} and {i,j} are connected.

Answer 1

[Nikolaos]

Ok, i made it. So, for a given matrix "pall" i go to a matrix "alpha(i,j,k,l)". For example: alpha(1,1,1,1)=pall(1,1)=1 alpha(2,2,2,2)=pall(4,4)=16 alpha(1,1,1,2)=pall(1,2)=2 .. p.s. If you have a faster solution please tell me. Thank you all

%this is the actual algorithm % pall=([1 2 3 4;5 6 7 8; 9 10 11 12; 13 14 15 16]); k=0 for n1=1:4 for n2=1:4 k=k+1 temp(k)=pall(n1,n2) end end k=0 alpha=zeros(2,2,2,2) for n3=1:2 for n4=1:2 for n5=1:2 for n6=1:2 k=k+1 alpha(n3,n4,n5,n6)=temp(k) end end end end %

[Nikolaos]

pall=([1 2 3 4;5 6 7 8; 9 10 11 12; 13 14 15 16]);

k=0

for n1=1:4

for n2=1:4

k=k+1

temp(k)=pall(n1,n2)

end

end

k=0

alpha=zeros(2,2,2,2)

for n3=1:2

for n4=1:2

for n5=1:2

for n6=1:2

k=k+1

alpha(n3,n4,n5,n6)=temp(k)

end

end

end

end

[Andrei Bobrov]

is better

permute(reshape(pall,[2 2 2 2]),[2,1,3,4])

[Jan]

@Nikolaos: Please use code-formatting either by starting the code lines with 2 spaces or by marking the code section with the mouse and hitting the "{} Code" button in this page.

[Nikolaos]

Ok thanks a lot.. what needs to be change if for example the pall matrix is larger? fe 16x16

[Walter Roberson]

Comments cannot be formatted yet, unfortunately.

Answer 2

[Friedrich]

Hi,

I am not sure what you mean with 4digit indexing. Do you want a 4d matrix?

    >> a = zeros(3,3,3,3);
    >> a(1,2,1,3)

    ans =

         0

Or do you like to pass 2 pairs of indices?

a = [1 2; 3 4]
%try to access 1,1 and 1,2
ind = sub2ind(size(a),[1 1],[1 2])
a(ind)

ans =

       1     2

[Nikolaos]

i want to access a matrix not by 2 digits indexing but by 4 index indexing. For example i want to map A(k,l,m,n)->p(i,j) {where i==row, j=column of p matrix }

Answer 3

[Jan]

One example:

A = rand(3, 4, 5, 6);
p = reshape(A, 12, 30);

disp(A(2,3,4,5))
disp(p(8, 24))

Does this match your needs? Then SUB2IND and IND2SUB might help.

[Nikolaos]

ok, i am a bit new to matlab, could be so kind of giving me an example using as a matrix the pall=([1 2 3 4;5 6 7 8; 9 10 11 12; 13 14 15 16])?

[Andrei Bobrov]

pall=[1 2 3 4;5 6 7 8; 9 10 11 12; 13 14 15 16]

a = zeros(2,2,2,2)

a(:) = pall

[Jan]

a = reshape(pall, 2,2,2,2);

[Nikolaos]

great thanks a lot

[Nikolaos]

but what if i have a matrix "pall" 100x100, or nxn .. ??

Thanx in andanve.