How can I create one vector x to have this function correct? x has to be the column vector k- 'th of A, from its diagonal to the end

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Victoria Ródenas 2019-12-11

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/496018-how-can-i-create-one-vector-x-to-have-this-function-correct-x-has-to-be-the-column-vector-k-th-o

评论： Ridwan Alam 2019-12-11

在 MATLAB Online 中打开

function [Q, R] = miqr(A)

[nr,nc]=size(A);

Q=eye(nr);

k=A(:,1:nc-1);

x=k(2:nr,nc); --> the error is here, it says "index in position 2 exceeds array bounds(musn not exceed 4)

H=Householder(VecHh(x));

P=blkdiag(1,H);

A=P*A;

Q=P*Q;

R=A;

Q=Q';

end

okay, thank you so much, i dont know what value of x i am expecting, the only request for my exercise is that x has to be the column vector k- 'th of A, from its diagonal to the end
the excercise is create one random array and then apply the function something like this :
>> A=rand(5)
A =
    0.8147    0.0975    0.1576    0.1419    0.6557
    0.9058    0.2785    0.9706    0.4218    0.0357
    0.1270    0.5469    0.9572    0.9157    0.8491
    0.9134    0.9575    0.4854    0.7922    0.9340
    0.6324    0.9649    0.8003    0.9595    0.6787
>> [Q, R] = miqr(A)
Index in position 2 exceeds array bounds (must not exceed 4).
Error in miqr (line 5)
x=k(2:nr,nc);
* but here is y error *
function A = Householder(v)
  %% Householder matrix of base v
  
  v = reshape(v,length(v),1);	% v is now a column vector
  A = eye(length(v)) - 2* v*v' /norm(v)^2;
end  

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Victoria Ródenas 2019-12-11

okay

Ridwan Alam 2019-12-11

what is k supposed to be? is it supposed to be an input to the miqr() like [Q,R]=miqr(A,k)?

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Answer 1

Ridwan Alam 2019-12-11

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/496018-how-can-i-create-one-vector-x-to-have-this-function-correct-x-has-to-be-the-column-vector-k-th-o#answer_405877

k has size nr x (nc-1). you are trying to assign x = k(2:nr,nc) which means the nc-th column of k. but k doesn't have nc-th column, it has nc-1 columns.

Now for me to debug more, you need to let me know what H=Householder(VecHh(x)) is doing and what size and value of x are you expecting.