Matrix manipulations

Hey all,

I'm having a bit of trouble calculating conditional proabbilities, say I have a matrix such as:

CgvB =

     0     0
     0     0
     0     0
     0     1
     0     1
     0     1
     0     1
     0     1
     0     1
     0     1
     1     0
     1     0
     1     1
     1     1

and I want to calculate the probability of having a 1 on the 2nd column given having a 1 on the first column in this case ists 2/14, but I'm using a script to automatically calculate all these probabilties. This is what I've started with: p=CgvB(length(CgvB(:,:)==1))/length(CgvB); this works but for empty matrices i get the error :Subscript indices must either be real positive integers or logicals. How can I perform these calculations without errors? Thanks for any help.

Answer 1

[Paulo Silva]

You can ensure that your array has the proper dimensions before doing the calculation

[sr,sc]=size(CgvB);
if (sr>0 & sc==2)
p=CgvB(length(CgvB(:,:)==1))/length(CgvB);
else
disp('The array must have at least one row and two columns');
end

[Ebrahim]

Thanks for that. Can I also just say after else, that p = []? This is because I don't want to display anything but just continue with my calculations.

[Paulo Silva]

yes you can give p some value when the arrays doesn't have the proper dimensions, it can also be done at the start of the code, give p a default value, you can use Inf or NaN instead of []