why doesn't my "if" statement work?

i have 2 columns that i am performing an element-wise foldchange analysis on columns A & B. if the result is less than 1 then the operation must be reversed. i have; 1. z=B./A % divide each element of B by corresponding A element 2. if z< 1 % if Z is less than 1 3. A./B*-1 % then divide A element by corresponding B element and multiply by -1 end

but i get no response from matlab. this should be easy but it's not. as always thanks for your time and input jb

Answer 1

[Wayne King]

You don't need an if statement, you can use logical indexing.

 A = randn(8,1);
 B = randn(8,1);
 Z = B./A; 
 Z(Z<1) = A(Z<1)./B(Z<1).*(-1);

[john borsellino]

wow!! i will give this a try thanks..(seconds later) thankyou wayne king for such a simple answer.logical indexing worked great.

Answer 2

[Mark]

The way you have it, you will only get the if statement to be satisfied if all elements of z are less than one. If you are trying to do this element by element, you could implement a loop through z to just change the ones that are <1.

[john borsellino]

hey mark, could you throw up some code, to explain the loop, thanks jb