How to calculate log(a/b) for each two rows at each column ?

I have a matrix mXn for example

a = 2 3 6 5 7 4

5 4 7 8 9 6

4 5 8 9 8 5

And from above 3X6 matrix i want to calculate log(second row/first rown) at each column

Then finally I will have 2X6 matrix

How can I solve for mXn matrix ?

I use this code

for i = 1:3
    for j = 1:6
        dlogd = log(a(i+1,j)/a(i,j));
    end
end

Answer 1

[Ameer Hamza]

a = ...
    [2 3 6 5 7 4
    5 4 7 8 9 6
    4 5 8 9 8 5];

b = log(a(2:end, :)./a(1:end-1,:));

Result

>> b
b =
    0.9163    0.2877    0.1542    0.4700    0.2513    0.4055
   -0.2231    0.2231    0.1335    0.1178   -0.1178   -0.1823

[John D'Errico]

Actually, no. You computed the ratio of the logs, not the log of the ratio.

In that case, a simple way to solve the problem is to just use diff on the log, since log(u/v) = log(u)-log(v).

diff(log(a))
ans =
      0.91629      0.28768      0.15415         0.47      0.25131      0.40547
     -0.22314      0.22314      0.13353      0.11778     -0.11778     -0.18232

[Ameer Hamza]

Oh! I misread that part. The solution is very concise by using diff().

[Jeevan Kumar Bodaballa]

Thank you

[John D'Errico]

It seemed clear this was just a slip of the brain.