SVD of a specific matrix and Singular values behaviour












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$begingroup$


I have a rectangular matrix $A in mathcal{M}_{l,n} (mathbb{C})$, $l>n$ which has this property :



$$A=left[begin{matrix} M_1 & i M_2 \ M_2 & -i M_1 end{matrix}right]$$



Where $M_i$ are (complex) rectangular matrices with same size $frac l 2 times frac n 2$.



Can i expect (formally) some special behaviour from the singular values of $A$ relatively to its size ?



Some Background :



Numerically, I noticed that the smallest singular values of $A$ are very close to $0$ relatively to the greatest ones when $n < l < 2n$ and not when $l ge 2n$. Then I found out that $A$ has that special structure described at the beginning of that question. I do expect a (quantitative) link between those two things.



My handwavy explanation is that, when $n < l < 2n$, the redundacy of information encoded by the special structure is well captured by the SVD, so we do not need all the eigenvalues to construct a good approximation of $A$.



Thank you.










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$endgroup$

















    2












    $begingroup$


    I have a rectangular matrix $A in mathcal{M}_{l,n} (mathbb{C})$, $l>n$ which has this property :



    $$A=left[begin{matrix} M_1 & i M_2 \ M_2 & -i M_1 end{matrix}right]$$



    Where $M_i$ are (complex) rectangular matrices with same size $frac l 2 times frac n 2$.



    Can i expect (formally) some special behaviour from the singular values of $A$ relatively to its size ?



    Some Background :



    Numerically, I noticed that the smallest singular values of $A$ are very close to $0$ relatively to the greatest ones when $n < l < 2n$ and not when $l ge 2n$. Then I found out that $A$ has that special structure described at the beginning of that question. I do expect a (quantitative) link between those two things.



    My handwavy explanation is that, when $n < l < 2n$, the redundacy of information encoded by the special structure is well captured by the SVD, so we do not need all the eigenvalues to construct a good approximation of $A$.



    Thank you.










    share|cite|improve this question









    $endgroup$















      2












      2








      2


      1



      $begingroup$


      I have a rectangular matrix $A in mathcal{M}_{l,n} (mathbb{C})$, $l>n$ which has this property :



      $$A=left[begin{matrix} M_1 & i M_2 \ M_2 & -i M_1 end{matrix}right]$$



      Where $M_i$ are (complex) rectangular matrices with same size $frac l 2 times frac n 2$.



      Can i expect (formally) some special behaviour from the singular values of $A$ relatively to its size ?



      Some Background :



      Numerically, I noticed that the smallest singular values of $A$ are very close to $0$ relatively to the greatest ones when $n < l < 2n$ and not when $l ge 2n$. Then I found out that $A$ has that special structure described at the beginning of that question. I do expect a (quantitative) link between those two things.



      My handwavy explanation is that, when $n < l < 2n$, the redundacy of information encoded by the special structure is well captured by the SVD, so we do not need all the eigenvalues to construct a good approximation of $A$.



      Thank you.










      share|cite|improve this question









      $endgroup$




      I have a rectangular matrix $A in mathcal{M}_{l,n} (mathbb{C})$, $l>n$ which has this property :



      $$A=left[begin{matrix} M_1 & i M_2 \ M_2 & -i M_1 end{matrix}right]$$



      Where $M_i$ are (complex) rectangular matrices with same size $frac l 2 times frac n 2$.



      Can i expect (formally) some special behaviour from the singular values of $A$ relatively to its size ?



      Some Background :



      Numerically, I noticed that the smallest singular values of $A$ are very close to $0$ relatively to the greatest ones when $n < l < 2n$ and not when $l ge 2n$. Then I found out that $A$ has that special structure described at the beginning of that question. I do expect a (quantitative) link between those two things.



      My handwavy explanation is that, when $n < l < 2n$, the redundacy of information encoded by the special structure is well captured by the SVD, so we do not need all the eigenvalues to construct a good approximation of $A$.



      Thank you.







      linear-algebra matrices matrix-decomposition svd singularvalues






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      asked Dec 14 '18 at 15:04









      nicomezinicomezi

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