How to make MATLAB ignore indices that are out of bounds for a matrix

I am working on a problem that involves the matrix A of size m,n.

if an element of A changes value, i want to make the elements next to it (left, top, right, and below) change value too if they have a certain value of their own.

when i now try to check the elements next to for example A(2,1), it will give me an error message because there exists no element A(2,0),

currently i can only think of a solution that uses many individual if statements for the outer regions of the matrix. which looks something like this:

if mi == 1
  if ni == 1                           %the element in the upper left corner
      if A(1,1) == 2
          if A(1,2) == value           %the element to the right of the upper left corner
             %change value of A(1,2)
          if A(2,1) == value
             %change value of A(2,1)   %the element below the upper left corner

and so on for all the elements that face the outside of the matrix...

Answer 1

[Sean de Wolski]

One way (of many):

Use min() and max() to figure out when the range is outside:

idx = -2:12; %indices outside of range 1:10
x = randperm(10); %10 values

Inside the range is less than or equal to the max of the size and greater than or equal to 1:

x(max(min(idx,size(x,2)),1))

[Jelmer]

thanks!

I am now using

if min(idx,size(x,2)) == max(1,idx)
  % code
end

[Sean de Wolski]

Looks good!

Just to point out size(x,2) is looking at the end of a row. If you're doing this for columns as well, use size(x,1) when identifying the max of a column.