if statement of type cell problem..

It seems an easy problem but I just can't figure it out.

let A,B,C be vectors.

 for i=1:100
 if A(i)<B(i)
 C(i)=0;
 else 
 C(i)=1;
 end
 end

this code, of course, works well. but if I define, say D={A(i)<B(i)} and

 for i=1:100
 if D{1}==1
 C(i)=0;
 else 
 C(i)=1;
 end
 end

This code does not work. Looks like some kind of data type problem, but I just don't know how to fix it. Thanks in advance.

Answer 1

[Geoff Hayes]

Check out the condition in the second block of code

 if D{1}==1

At each iteration, the code is comparing the first element of the cell array D with 1 when it should be considering each element of D. But I suspect that won't work either because of the way that D was initialized.

What is the code for that initialization? Was it simply

 D = {A<B}

which is different from (but similar to) your example of D={A(i)<B(i)}. In the case of D = {A<B}, D is just a single element cell array with the first element being a logical vector of dimension mx1 (where m is the length of the vectors A and B). So accessing

 D{1}

returns a mx1 logical array which can't be compared to the single digit one.

What you want to do instead is initialize D as follows

 D = A<B;

which will be a mx1 array/vector of logical elements where a 1 in the ith position indicates that A(i)<B(i) and a zero indicates the opposite.

Your second block of code then becomes

 D = A<B;
 for k=1:100
     if D(k)==1
         C(k)=0;
     else 
         C(k)=1;
     end
 end

Try the above and see what happens!

[Shi-hyung Lee]

Thanks. It works. But I'm wondering if I have to compare, let's say A(i) with B(i-1), E(i) with B(i-2), F(i) with B(i-3) and so on. how can I do this?

[Geoff Hayes]

I think your first approach was just as elegant - to me, there does not seem to be any need to create a D vector. Just use the comparison as

 if A(i)<B(i)

Then, as you add more conditions, say for A(i) with B(i-1) you can build them into your if and (maybe) else if statements.

[Shi-hyung Lee]

What I'm doing is like this.

 Z={A<B C<D E<F};
for k=1:3
for i=1:100
if Z{k}(i)==1
X(i)=0;
else
X(i)=1;
end
end
name=['Result', num2str(k)];
xlswrite(name,X);
end

I guess there are not much differences in time and effort between doing manually and doing like this. But I just want to do it this way. That's all.

[Shi-hyung Lee]

Solved the problem. I just have to do A(1:100)>B(2:101) and such things... What a fool I am..