Issue using sum() for QR method script

Question

Chris 2016-10-3

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/305596-issue-using-sum-for-qr-method-script

编辑： Brandon Eidson 2016-12-29

The following is a cut-out from a QR method script for finding all the eigenvalues of a matrix. When the line for a(:,i)=.... is run within the 'for' loop it fails to complete. I am trying to mimic the expression from the image below with a(:,i) and having a lot of trouble, please help me.

 A=[8 -2 -2; -2 4 -2; -2 -2 13]; %initial matrix
 k=0; %starts iteration count
 while ((max(abs((lambdak-lambda0)/lambda0))>toler) && (k<maxiter)); %as long as the change between the previous and current lamda are >toler, keep going until you hit the iteration limit
    lambda0=lambdak; %establish baseline values for lamda
    k=k+1; %iteration number for display +1
    a=A;    
    q(:,1)=a(:,1)./norm(a(:,1));    
    for i=2:n        
        a_p(:,i)=a(:,i)-sum(transpose(q(:,i-1))*a(:,i).*q(:,i-1),i,1,i-1)  %where I am getting stuck
        q(:,i)=a_p(:,i)./norm(a_p(:,i))
    end
 end

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Answer 1

Brandon Eidson 2016-10-7

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https://ww2.mathworks.cn/matlabcentral/answers/305596-issue-using-sum-for-qr-method-script#answer_238012

编辑：Brandon Eidson 2016-12-29

Hey Chris,

It looks to me that your implementation of the "sum" function is incorrect. This function only takes two inputs, but I think you are passing it four inputs. See the documentation at the link below.

http://www.mathworks.com/help/releases/R2016a/matlab/ref/sum.html