Could someone explain below code

I have code like following

for i = 1:rce(2)
   for j = 1:rce(1)
  if i == 1 & j == 1
     mnn(jj,1:4) = [1 rce(1)+2 rce(1)+3 2];
     jj = jj + 1;
  elseif i ~= 1 & j == 1
     mnn(jj,:) = mnn(jj-1,1:4) + 2;
     jj = jj + 1;
  end
  if j > 1
     mnn(jj,:) = mnn(jj-1,1:4) + 1;
     jj = jj + 1;
  end
   end
end

Could someone explain below part for me? What is it for

mnn(jj,:) = mnn(jj-1,1:4) + 2;

and

mnn(jj,:) = mnn(jj-1,1:4) + 1;

Best regards

Answer 1

[Azzi Abdelmalek]

% just trie these to understand

A=[1 2 3;4 5 6;7 8 9]
A(1:2,:) 
% 1:2 means line 1 to line 2 , 
%  :  means all columns

 A(:,2:3)  %means all lines , and column 2 to column 3

Answer 2

[Wayne King]

Without more context it's hard to say exactly what it's for, but it is simply replacing the jj-th row of mnn with the jj-1 row and adding 2 to each element.

jj must be at least 2 and I'm not sure why they used 1:4 on the RHS because mnn must have only 4 columns.

mnn = randn(4,4);
jj = 2;
mnn(jj,:) = mnn(jj-1,1:4)+2;

You could have just written:

mnn(jj,:) = mnn(jj-1,:)+2;

You should see that the 2nd row is simply the first row with 2 added to each element of the row vector.

The last line simply adds 1.