Question

I have a mask with a certain numbers of rows and columns.
I would like to read just the (i,j) components that contains for example 1.
Then once the (i,j) component with 1 is found perform four different action if any of the (i+1,j),(i-i,j),(i,j+1),(i,j-1) equal to 1 is found.

Hope this is clear.
Any advice are welcome.
Thanks.

Answer 1

Let your mask be something like this:

integer, dimension(1:r,1:c) :: mask

Then the following fragment should point you in the right direction:

forall (i=1:r, j=1:c, mask(i,j)==1)
   if ( mask(i-1,j)==1) then
      ! do the right thing
   else if ( mask(i+1,j)==1) then
      ! I hope you get the picture now
...

I’ll leave it to you to deal with the edge cases where +/- i/j step outside the array bounds. forall is not necessarily the fastest construction to use, and we could debate the elegance and readability of using it rather than a sequence of loops, but let’s not.