Skipping calculations using if

Hello,

I have the following code:

for j = 1:(length(acalc)-1)

    for ii = (j+1):length(acalc)

    dotp(count2,:) = dot(acalc(j,:),acalc(ii,:));
    magp(count2,:) = mag(j)*mag(ii);

    count2 = count2 + 1;  
    end
end

Which works fine if length(acalc) > 1. However when length(acalc) = 1 (as it sometimes is), an error is returned presumably because of the failure in accessing acalc(ii,:) = acalc(j+1,:) = acalc(2,:)

Could someone help me resolve this issue? i.e. by simply skipping the calculations if length(acalc) = 1?

I tried simply stating if length(acalc) > 1 before this section of code, but that didn't seem to work.

Many thanks,

Tom

Answer 1

[Matt J]

No, if length(acalc)=1, the code you've shown would never be executed. For example, running the following will not result in anything displayed.

acalc=10;

for j = 1:(length(acalc)-1)

   disp 'Executing'

end

[Tom]

Ok. Well the error being returned is:

"Attempted to access acalc(2,:); index out of bounds because size(acalc)=[1,3]."

Does that not seem to imply that the way I've written the code is asking it to access a row of acalc which doesn't exist?

[Matt J]

Yes. Since acalc is 1x3 it has one row, but you are trying to access a second row acalc(2,:).

[Tom]

I thought that was the problem. But the problem is that most of the time (that section of the code is within a loop of its own) acalc consists of 4 or more rows and then everything is fine. What would be the way to skip those calculations for when acalc consists of only 1 row? I thought it would simply be if length(acalc) = 1 ... end. But that didn't work...

[Matt J]

It doesn't look like length(acalc) is the command you should be using if you really intend to measure the number of rows. You should be using size(acalc,1) instead.