Using Sum(W) ==1 as a condition in a function

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Andrew
Andrew on 19 Jul 2013
I have to write [sum(W) should equal 1] within a function. W is an 8 element vector.
When I try to write: if sum(W)==1
the function stops working. I have tried many variations of this but none of them work. Currently the sum of W is equal to 1.
How can I put this condition in the function?
  4 Comments
Andrew
Andrew on 20 Jul 2013
The following is the error message:
Error in RARvariance1 (line 19) T=length(A); %Time period, the same for all assets
Output argument "RARV" (and maybe others) not assigned during call to "C:\Users

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Answers (3)

nl2605
nl2605 on 19 Jul 2013
I think all you need to do is to pass the value A,B,C,D,E,F,G,H,W when you call this function. It has got nothing to do with sum. Also, the code that you have posted here has a semi-colon after if statement which is wrong. If its just a typo then its ok.
  6 Comments
Muthu Annamalai
Muthu Annamalai on 22 Jul 2013
sum(W) == 1 may involve some floating point comparison issues depending on the type of variable W. Without the full invocation code of function RARvariance1 we I cannot speculate on that.

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Image Analyst
Image Analyst on 20 Jul 2013
For some reason your function is returning before it ever gets to the "RARV=-(ER)/sqrt(V);" line so RARV (which is required to be defined because it needs to be returned) never gets defined.
I have an idea - why don't you use the debugger to step through your code? http://blogs.mathworks.com/videos/2012/07/03/debugging-in-matlab/ You will quickly see which lines of code get executed and which don't.
  1 Comment
Image Analyst
Image Analyst on 20 Jul 2013
That's too bad. Debugging is a skill you should be able to learn. If you click in the margin and get the red spot on the first line in the function, the click F5 to run your program, when is stops at the red spot, you'll see that you don't have SW less than 1 so you go into the "else" block. Unfortunately you have no code in there, thus RARV never gets assigned to any value. What do you want to happen if SW > 1? Whatever it is, put that code after the else and make sure you assign some value for RARV.

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Muthu Annamalai
Muthu Annamalai on 22 Jul 2013
@Andrew on the similar lines as @Image Analyst - I think your return value is not assigned because you don't enter the if-condition branch.
So why don't you replace the code, using an assertion, and eliminating the if-else-end statement.
function RARV=RARvariance1(A,B,C,D,E,F,G,H,W)
T=length(A); %Time period, the same for all assets SW=sum(W);
assert( abs( SW - 1.0000) < 1e-3, 'sum(W) does not add to 1')
DD=[A-mean(A), B-mean(B), C-mean(C), D-mean(D), E-mean(E), F-mean(F), G-mean(G), H-mean(H)]; %Temporal, needed for covariances
Cov=DD'*DD/T;
V=W(1,:)*Cov*W(1,:)';
%Portfolio expected returns
ER=[mean(A), mean(B), mean(C), mean(D), mean(E), mean(F), mean(G), mean(H)]*W(1,:)';
%(Negative) risk adjusted return
RARV=-(ER)/sqrt(V); %Change V to sqrt(V) for semi-standard deviation
end

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