diff and 3D-matrix

Dear all, I am reverse engineering a piece of the data evaluation code that is used in my university/ workgroup and i have a hard time understanding what seems to be a simple thing. I do understand what the output should be hover.The code is inside a loop but for now i just need to figure out what those two lines do in principle?

       Fx(1:size(my_matrix,1)-1,i,j)=diff(my_matrix(:,i,j)/(a_scalar_dimension/1000));
       Fx(size(my_matrix,1),i,j)=0;

Thank you very much in advance

Answer 1

[Star Strider]

The first assignment:

       Fx(1:size(my_matrix,1)-1,i,j)=diff(my_matrix(:,i,j)/(a_scalar_dimension/1000));

simply seems to take the consecutive differences (using the diff funciton) over the rows of ‘my_matrix’ for the fixed second and third dimensions ‘i’ and ‘j’. We can assume this is in a nested loop of some design.

The second assignment:

       Fx(size(my_matrix,1),i,j)=0;

sets the last element of ‘Fx’ for the same ‘i’ and ‘j’ coordinates to zero, apparently to equalise the row sizes of ‘Fx’ and ‘my_matrix’. In recent MATLAB versions, using end in place of the size call would have the same effect:

       Fx(end+1,i,j)=0;

That’s my best guess, anyway.