How to find the element in on boundary or interior?

a=[3 4 5;6 1 2]

I want to know if the element 2 is on boundary or interior?

how will i check?

[Image Analyst]

When a is a 2 by 3 matrix:

a =
     3     4     5
     6     1     2

Exactly which pixels do you consider to be interior and which to be exterior/boundary? The all look like boundary pixels to me.

[Jos (10584)]

Boundary of what ?

Answer 1

[Jos (10584)]

tf = false(size(a)) 
tf(2:end-1,2:end-1) = true 

a(tf) % elements in interior
a(~tf) % elements on boundary

Answer 2

[Image Analyst]

What is element 2? The lower right element with the value of 2? Or row=2, column = 1 which is how the column major order of MATLAB defines the second element? Can't you just look at the row and column and see if it's equal to 1 or the total number of rows or columns in the matrix?

Answer 3

[Alberto]

If you suppose there is only one value 2 in the matrix, this code may be useful:

a=[3 4 5;6 2 1; 1 6 9] % interior value % a=[3 4 5;6 1 2; 1 6 9] % edge value [nrow ncol]= size(a) % Obtain dimensions

% find(a==2) extract linear index, so you better convert to subindices [I,J] = ind2sub(size(a),find(a==2))

% and checking if I==1 J==1 I==nrow J==ncol display('In the edge') else display('interior value')

end

% If there are other 2 values you should create a for across the I and J vectors.

a=[3 4 5;6 2 1; 2 6 9];

[nrow ncol]= size(a); [I,J] = ind2sub(size(a),find(a==2));

for k=1:length(I) if I(k)==1 J(k)==1 I(k)==nrow J(k)==ncol display(['In the edge ( ', num2str(I(k)), ', ', num2str(J(k)), ' )'])

else display(['Interior value ( ', num2str(I(k)), ', ', num2str(J(k)), ' )'])

end

end

[Anusha]

a=[3 4 5; 6 7 8; 9 0 1]

if i want to identify the element to check if the element is boundary or interior

This example 7 is a interior node and other element are boundary

How to check this node