How can I loop with two variables, can't figure it out

I am totally new to Matlab, and my master thesis require me to use matlab to do some analysis. I had a problem with loop. I wanna construct a loop with two variables for example

    for i = 2:4
     for j = 1:4
       Ratio = Price(i,:)/Vol(j,:)
    end
    end

Price = 1 2 3 4 
        5 6 7 8
        9 8 9 6

Vol   = 2 3 4 5
        6 7 8 9
        1 2 3 4

and I want my answer to be

ratio = 2.5 2.0 1.8 1.6
        1.5 1.1 1.1 0.7

The 2nd row of Price divide by the 1st row of Vol The 3rd row of Price divide by the 2st row of Vol and so on ...........until the end row of price then stop the loop.

Can it work if price and Vol has different number of row but they have some number of Column?

[Stephen23]

Note that you should not use the variable names i and j, as these are the names of the inbuilt imaginary unit.

[Matt J]

That's not a big issue anymore, now that the syntax 1i and 1j are supported,

      >> for i=1:3, i+1i, end

      ans =

         1.0000 + 1.0000i

      ans =

         2.0000 + 1.0000i

      ans =

         3.0000 + 1.0000i

Answer 1

[Matt J]

Just do

    Ratio=Price(2:4,:)./Vol(1:3,:)

[Matt J]

Can it work if price and Vol has different number of row but they have some number of Column?

If Vol has more rows than Price, then some rows of Vol wouldn't get used in the computation you've described. Just throw those rows away, or extract them as I have done above.

[Matt J]

With a loop, it would look like the following. You don't need 2 loop variables

     for i = 1:size(P,1)-1

       Ratio(i,:) = Price(i,:)./Vol(i+1,:)

    end

[Steven Kwok]

ThANK Matt I try to use the first method, but it show out the remark Error using ./ Matrix dimensions must agree.

Did I do anything wrong??

[Matt J]

You probably applied it to a matrix with fewer than 4 rows. When I try it works fine:

     >> Price=rand(4), Vol=rand(4)

    Price =

        0.0945    0.9295    0.1693    0.4406
        0.4041    0.5263    0.2589    0.9677
        0.0103    0.3618    0.3235    0.4030
        0.2918    0.7204    0.6432    0.9690

    Vol =

        0.8800    0.4943    0.8787    0.3100
        0.1134    0.6626    0.7284    0.0347
        0.9363    0.1531    0.8292    0.2951
        0.0421    0.4184    0.7025    0.4976

    >> Ratio=Price(2:4,:)./Vol(1:3,:)

    Ratio =

        0.4592    1.0647    0.2946    3.1215
        0.0909    0.5461    0.4441   11.6190
        0.3116    4.7041    0.7757    3.2835

[Steven Kwok]

Thank Matt, it works well with the loop method!

[Matt J]

The non-loop method works well, too !

[Steven Kwok]

another question, I am not sure whether it is looping or not since in the workspace, the variable ratio contain only one row. please help

[Steven Kwok]

when I first input the code to the command box it show a series of result. It is actually looping. But when I look at the workspace, it shows only 1xN matrix. I couldn't further moving average it vertically because it contain one row.

meanratio = tsmovavg(Ratio,'s',2,1)

[Stephen23]

@Steven Kwok: learn about vectorized code in MATLAB.

Matt J has shown in his answer how to do this calculation without loops, and this is the best way to solve your problem in MATLAB. Do not use loops for doing this calculation.

[Matt J]

@Steven Kwok,

I don't know why you prefer the looping method. You seem to be having trouble modifying my vectorized proposal for different sizes. Here it is again, a bit more generalized

     n=size(P,1);
    Ratio=Price(1:n-1,:)./Vol(2:n,:);

[Steven Kwok]

Thank you all for your suggestion. I didn't prefer any method over the other. I use it just now only because only the looping method work on my machine. I am reading the vectorized code in matlab and I will try it again on my calculation.

[Steven Kwok]

I made it! Thank guys for your kind support.

[Matt J]

Great. Could you hit this button, if you like the answer you got?