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Rewriting a quadratic Matrix equation as a quadratic vector equation
Convexity of a complicated functionExpressing Quadratic Form for a Matrix Inverse using Summation SymbolsFull Rank Matrix with a specific constructionMatrix Multiplication - Product of [Row or Column Vector] and Matrix [Lay P94, Strang P59]How to calculate a vector of quadratic forms (matrix algebra)Conditions to preserve Laplacian matrixBuilding matrix so that the inner product of columns results in an element of another matrixMatrix with only real eigenvalues is similar to upper triangular matrixNumerator layout for derivatives and the chain ruleHelp to find a factorization of a matrix into a product and sum of matricesRepresentation of a matrix (tensor)
$begingroup$
Consider the set of $N times N$ matrices $W_i_i=1^i=L$, set of $N times 1$ vectors $g_i_i=1^i=L$ and $h_i_i=1^i=L$. Now consider the following sum
beginalign
S=sum_isum_jg_i^HW_ih_ih_j^HW_j^Hg_j
endalign
where the summation runs through all $L$ for all $i,j$. Clearly, this equation is quadratic in the matrix variables $W_i_i=1^i=L$. Now define the column vector
beginalign
w=beginbmatrix operatornamevec(W_1) \ operatornamevec(W_2) \ vdots \ operatornamevec(W_L) endbmatrix
endalign
where for a matrix $A$, $operatornamevec(A)$ denotes the column vector containing the columns of $A$ starting from the first column. The question is, can we write
beginalign
S=w^HQw
endalign
where $Q$ is a matrix which is a function of $g_i_i=1^i=L$ and $h_i_i=1^i=L$. If so, what is the structure of $Q$?
linear-algebra matrices convex-optimization quadratic-forms block-matrices
$endgroup$
add a comment |
$begingroup$
Consider the set of $N times N$ matrices $W_i_i=1^i=L$, set of $N times 1$ vectors $g_i_i=1^i=L$ and $h_i_i=1^i=L$. Now consider the following sum
beginalign
S=sum_isum_jg_i^HW_ih_ih_j^HW_j^Hg_j
endalign
where the summation runs through all $L$ for all $i,j$. Clearly, this equation is quadratic in the matrix variables $W_i_i=1^i=L$. Now define the column vector
beginalign
w=beginbmatrix operatornamevec(W_1) \ operatornamevec(W_2) \ vdots \ operatornamevec(W_L) endbmatrix
endalign
where for a matrix $A$, $operatornamevec(A)$ denotes the column vector containing the columns of $A$ starting from the first column. The question is, can we write
beginalign
S=w^HQw
endalign
where $Q$ is a matrix which is a function of $g_i_i=1^i=L$ and $h_i_i=1^i=L$. If so, what is the structure of $Q$?
linear-algebra matrices convex-optimization quadratic-forms block-matrices
$endgroup$
add a comment |
$begingroup$
Consider the set of $N times N$ matrices $W_i_i=1^i=L$, set of $N times 1$ vectors $g_i_i=1^i=L$ and $h_i_i=1^i=L$. Now consider the following sum
beginalign
S=sum_isum_jg_i^HW_ih_ih_j^HW_j^Hg_j
endalign
where the summation runs through all $L$ for all $i,j$. Clearly, this equation is quadratic in the matrix variables $W_i_i=1^i=L$. Now define the column vector
beginalign
w=beginbmatrix operatornamevec(W_1) \ operatornamevec(W_2) \ vdots \ operatornamevec(W_L) endbmatrix
endalign
where for a matrix $A$, $operatornamevec(A)$ denotes the column vector containing the columns of $A$ starting from the first column. The question is, can we write
beginalign
S=w^HQw
endalign
where $Q$ is a matrix which is a function of $g_i_i=1^i=L$ and $h_i_i=1^i=L$. If so, what is the structure of $Q$?
linear-algebra matrices convex-optimization quadratic-forms block-matrices
$endgroup$
Consider the set of $N times N$ matrices $W_i_i=1^i=L$, set of $N times 1$ vectors $g_i_i=1^i=L$ and $h_i_i=1^i=L$. Now consider the following sum
beginalign
S=sum_isum_jg_i^HW_ih_ih_j^HW_j^Hg_j
endalign
where the summation runs through all $L$ for all $i,j$. Clearly, this equation is quadratic in the matrix variables $W_i_i=1^i=L$. Now define the column vector
beginalign
w=beginbmatrix operatornamevec(W_1) \ operatornamevec(W_2) \ vdots \ operatornamevec(W_L) endbmatrix
endalign
where for a matrix $A$, $operatornamevec(A)$ denotes the column vector containing the columns of $A$ starting from the first column. The question is, can we write
beginalign
S=w^HQw
endalign
where $Q$ is a matrix which is a function of $g_i_i=1^i=L$ and $h_i_i=1^i=L$. If so, what is the structure of $Q$?
linear-algebra matrices convex-optimization quadratic-forms block-matrices
linear-algebra matrices convex-optimization quadratic-forms block-matrices
edited yesterday
Rócherz
2,8912821
2,8912821
asked Apr 1 '13 at 17:30
dineshdileepdineshdileep
5,98611935
5,98611935
add a comment |
add a comment |
1 Answer
1
active
oldest
votes
$begingroup$
beginalign
S&=sum_isum_jg_i^HW_ih_ih_j^HW_j^Hg_j\
&=sum_isum_joperatornametrace(g_jg_i^HW_ih_ih_j^HW_j^H)\
&=sum_isum_joperatornamevec(W_j)^H operatornamevec(g_jg_i^HW_ih_ih_j^H)\
&qquadqquadqquadbecause operatornametrace(AB^H)=operatornametrace(A^HB)=operatornamevec(A)^Hoperatornamevec(B)\
& \
&=sum_isum_joperatornamevec(W_j)^H left((h_ih_j^H)^Totimes(g_jg_i^H)right)operatornamevec(W_i)\
&qquadqquadqquadbecause operatornamevec(ABC)=(C^Totimes A)operatornamevec(B)\
& \
&=sum_isum_joperatornamevec(W_j)^H left((barh_jh_i^T)otimes(g_jg_i^H)right)operatornamevec(W_i)\
&=w^H Qw,
endalign
where $Q$ is a block matrix whose $(j,i)$-th (note: not $(i,j)$-th) subblock is $(barh_jh_i^T)otimes(g_jg_i^H)$.
$endgroup$
$begingroup$
you are always reliable!!!
$endgroup$
– dineshdileep
Apr 2 '13 at 8:50
$begingroup$
@dineshdileep What? Who knows if some mistakes are lurking around in some shadowy places. You should double-check the claimed result.
$endgroup$
– user1551
Apr 2 '13 at 16:12
$begingroup$
I will definitely do that.
$endgroup$
– dineshdileep
Apr 3 '13 at 4:17
$begingroup$
Can you explain (mathematically) the second last step, where you switch to the block matrix. (I almost have it intuitively, but would like to know a rigorous one).
$endgroup$
– dineshdileep
Apr 3 '13 at 4:46
1
$begingroup$
Let $w_j=operatornamevec(W_j)$. Then $w^T=(w_1^T,ldots,w_n^T)$. Partition $Q$ into subblocks, each of size $ntimes n$. Call the $(j,i)$-th block $Q_ji$. Then by $w^HQw=sum_isum_j w_j^H Q_ji w_i$. So, by comparing coefficients, we should set $Q_ji=(barh_jh_i^T)otimes(g_jg_i^H)$.
$endgroup$
– user1551
Apr 3 '13 at 20:51
|
show 1 more comment
Your Answer
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1 Answer
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oldest
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1 Answer
1
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active
oldest
votes
$begingroup$
beginalign
S&=sum_isum_jg_i^HW_ih_ih_j^HW_j^Hg_j\
&=sum_isum_joperatornametrace(g_jg_i^HW_ih_ih_j^HW_j^H)\
&=sum_isum_joperatornamevec(W_j)^H operatornamevec(g_jg_i^HW_ih_ih_j^H)\
&qquadqquadqquadbecause operatornametrace(AB^H)=operatornametrace(A^HB)=operatornamevec(A)^Hoperatornamevec(B)\
& \
&=sum_isum_joperatornamevec(W_j)^H left((h_ih_j^H)^Totimes(g_jg_i^H)right)operatornamevec(W_i)\
&qquadqquadqquadbecause operatornamevec(ABC)=(C^Totimes A)operatornamevec(B)\
& \
&=sum_isum_joperatornamevec(W_j)^H left((barh_jh_i^T)otimes(g_jg_i^H)right)operatornamevec(W_i)\
&=w^H Qw,
endalign
where $Q$ is a block matrix whose $(j,i)$-th (note: not $(i,j)$-th) subblock is $(barh_jh_i^T)otimes(g_jg_i^H)$.
$endgroup$
$begingroup$
you are always reliable!!!
$endgroup$
– dineshdileep
Apr 2 '13 at 8:50
$begingroup$
@dineshdileep What? Who knows if some mistakes are lurking around in some shadowy places. You should double-check the claimed result.
$endgroup$
– user1551
Apr 2 '13 at 16:12
$begingroup$
I will definitely do that.
$endgroup$
– dineshdileep
Apr 3 '13 at 4:17
$begingroup$
Can you explain (mathematically) the second last step, where you switch to the block matrix. (I almost have it intuitively, but would like to know a rigorous one).
$endgroup$
– dineshdileep
Apr 3 '13 at 4:46
1
$begingroup$
Let $w_j=operatornamevec(W_j)$. Then $w^T=(w_1^T,ldots,w_n^T)$. Partition $Q$ into subblocks, each of size $ntimes n$. Call the $(j,i)$-th block $Q_ji$. Then by $w^HQw=sum_isum_j w_j^H Q_ji w_i$. So, by comparing coefficients, we should set $Q_ji=(barh_jh_i^T)otimes(g_jg_i^H)$.
$endgroup$
– user1551
Apr 3 '13 at 20:51
|
show 1 more comment
$begingroup$
beginalign
S&=sum_isum_jg_i^HW_ih_ih_j^HW_j^Hg_j\
&=sum_isum_joperatornametrace(g_jg_i^HW_ih_ih_j^HW_j^H)\
&=sum_isum_joperatornamevec(W_j)^H operatornamevec(g_jg_i^HW_ih_ih_j^H)\
&qquadqquadqquadbecause operatornametrace(AB^H)=operatornametrace(A^HB)=operatornamevec(A)^Hoperatornamevec(B)\
& \
&=sum_isum_joperatornamevec(W_j)^H left((h_ih_j^H)^Totimes(g_jg_i^H)right)operatornamevec(W_i)\
&qquadqquadqquadbecause operatornamevec(ABC)=(C^Totimes A)operatornamevec(B)\
& \
&=sum_isum_joperatornamevec(W_j)^H left((barh_jh_i^T)otimes(g_jg_i^H)right)operatornamevec(W_i)\
&=w^H Qw,
endalign
where $Q$ is a block matrix whose $(j,i)$-th (note: not $(i,j)$-th) subblock is $(barh_jh_i^T)otimes(g_jg_i^H)$.
$endgroup$
$begingroup$
you are always reliable!!!
$endgroup$
– dineshdileep
Apr 2 '13 at 8:50
$begingroup$
@dineshdileep What? Who knows if some mistakes are lurking around in some shadowy places. You should double-check the claimed result.
$endgroup$
– user1551
Apr 2 '13 at 16:12
$begingroup$
I will definitely do that.
$endgroup$
– dineshdileep
Apr 3 '13 at 4:17
$begingroup$
Can you explain (mathematically) the second last step, where you switch to the block matrix. (I almost have it intuitively, but would like to know a rigorous one).
$endgroup$
– dineshdileep
Apr 3 '13 at 4:46
1
$begingroup$
Let $w_j=operatornamevec(W_j)$. Then $w^T=(w_1^T,ldots,w_n^T)$. Partition $Q$ into subblocks, each of size $ntimes n$. Call the $(j,i)$-th block $Q_ji$. Then by $w^HQw=sum_isum_j w_j^H Q_ji w_i$. So, by comparing coefficients, we should set $Q_ji=(barh_jh_i^T)otimes(g_jg_i^H)$.
$endgroup$
– user1551
Apr 3 '13 at 20:51
|
show 1 more comment
$begingroup$
beginalign
S&=sum_isum_jg_i^HW_ih_ih_j^HW_j^Hg_j\
&=sum_isum_joperatornametrace(g_jg_i^HW_ih_ih_j^HW_j^H)\
&=sum_isum_joperatornamevec(W_j)^H operatornamevec(g_jg_i^HW_ih_ih_j^H)\
&qquadqquadqquadbecause operatornametrace(AB^H)=operatornametrace(A^HB)=operatornamevec(A)^Hoperatornamevec(B)\
& \
&=sum_isum_joperatornamevec(W_j)^H left((h_ih_j^H)^Totimes(g_jg_i^H)right)operatornamevec(W_i)\
&qquadqquadqquadbecause operatornamevec(ABC)=(C^Totimes A)operatornamevec(B)\
& \
&=sum_isum_joperatornamevec(W_j)^H left((barh_jh_i^T)otimes(g_jg_i^H)right)operatornamevec(W_i)\
&=w^H Qw,
endalign
where $Q$ is a block matrix whose $(j,i)$-th (note: not $(i,j)$-th) subblock is $(barh_jh_i^T)otimes(g_jg_i^H)$.
$endgroup$
beginalign
S&=sum_isum_jg_i^HW_ih_ih_j^HW_j^Hg_j\
&=sum_isum_joperatornametrace(g_jg_i^HW_ih_ih_j^HW_j^H)\
&=sum_isum_joperatornamevec(W_j)^H operatornamevec(g_jg_i^HW_ih_ih_j^H)\
&qquadqquadqquadbecause operatornametrace(AB^H)=operatornametrace(A^HB)=operatornamevec(A)^Hoperatornamevec(B)\
& \
&=sum_isum_joperatornamevec(W_j)^H left((h_ih_j^H)^Totimes(g_jg_i^H)right)operatornamevec(W_i)\
&qquadqquadqquadbecause operatornamevec(ABC)=(C^Totimes A)operatornamevec(B)\
& \
&=sum_isum_joperatornamevec(W_j)^H left((barh_jh_i^T)otimes(g_jg_i^H)right)operatornamevec(W_i)\
&=w^H Qw,
endalign
where $Q$ is a block matrix whose $(j,i)$-th (note: not $(i,j)$-th) subblock is $(barh_jh_i^T)otimes(g_jg_i^H)$.
edited yesterday
Rócherz
2,8912821
2,8912821
answered Apr 1 '13 at 18:13
user1551user1551
73.5k566129
73.5k566129
$begingroup$
you are always reliable!!!
$endgroup$
– dineshdileep
Apr 2 '13 at 8:50
$begingroup$
@dineshdileep What? Who knows if some mistakes are lurking around in some shadowy places. You should double-check the claimed result.
$endgroup$
– user1551
Apr 2 '13 at 16:12
$begingroup$
I will definitely do that.
$endgroup$
– dineshdileep
Apr 3 '13 at 4:17
$begingroup$
Can you explain (mathematically) the second last step, where you switch to the block matrix. (I almost have it intuitively, but would like to know a rigorous one).
$endgroup$
– dineshdileep
Apr 3 '13 at 4:46
1
$begingroup$
Let $w_j=operatornamevec(W_j)$. Then $w^T=(w_1^T,ldots,w_n^T)$. Partition $Q$ into subblocks, each of size $ntimes n$. Call the $(j,i)$-th block $Q_ji$. Then by $w^HQw=sum_isum_j w_j^H Q_ji w_i$. So, by comparing coefficients, we should set $Q_ji=(barh_jh_i^T)otimes(g_jg_i^H)$.
$endgroup$
– user1551
Apr 3 '13 at 20:51
|
show 1 more comment
$begingroup$
you are always reliable!!!
$endgroup$
– dineshdileep
Apr 2 '13 at 8:50
$begingroup$
@dineshdileep What? Who knows if some mistakes are lurking around in some shadowy places. You should double-check the claimed result.
$endgroup$
– user1551
Apr 2 '13 at 16:12
$begingroup$
I will definitely do that.
$endgroup$
– dineshdileep
Apr 3 '13 at 4:17
$begingroup$
Can you explain (mathematically) the second last step, where you switch to the block matrix. (I almost have it intuitively, but would like to know a rigorous one).
$endgroup$
– dineshdileep
Apr 3 '13 at 4:46
1
$begingroup$
Let $w_j=operatornamevec(W_j)$. Then $w^T=(w_1^T,ldots,w_n^T)$. Partition $Q$ into subblocks, each of size $ntimes n$. Call the $(j,i)$-th block $Q_ji$. Then by $w^HQw=sum_isum_j w_j^H Q_ji w_i$. So, by comparing coefficients, we should set $Q_ji=(barh_jh_i^T)otimes(g_jg_i^H)$.
$endgroup$
– user1551
Apr 3 '13 at 20:51
$begingroup$
you are always reliable!!!
$endgroup$
– dineshdileep
Apr 2 '13 at 8:50
$begingroup$
you are always reliable!!!
$endgroup$
– dineshdileep
Apr 2 '13 at 8:50
$begingroup$
@dineshdileep What? Who knows if some mistakes are lurking around in some shadowy places. You should double-check the claimed result.
$endgroup$
– user1551
Apr 2 '13 at 16:12
$begingroup$
@dineshdileep What? Who knows if some mistakes are lurking around in some shadowy places. You should double-check the claimed result.
$endgroup$
– user1551
Apr 2 '13 at 16:12
$begingroup$
I will definitely do that.
$endgroup$
– dineshdileep
Apr 3 '13 at 4:17
$begingroup$
I will definitely do that.
$endgroup$
– dineshdileep
Apr 3 '13 at 4:17
$begingroup$
Can you explain (mathematically) the second last step, where you switch to the block matrix. (I almost have it intuitively, but would like to know a rigorous one).
$endgroup$
– dineshdileep
Apr 3 '13 at 4:46
$begingroup$
Can you explain (mathematically) the second last step, where you switch to the block matrix. (I almost have it intuitively, but would like to know a rigorous one).
$endgroup$
– dineshdileep
Apr 3 '13 at 4:46
1
1
$begingroup$
Let $w_j=operatornamevec(W_j)$. Then $w^T=(w_1^T,ldots,w_n^T)$. Partition $Q$ into subblocks, each of size $ntimes n$. Call the $(j,i)$-th block $Q_ji$. Then by $w^HQw=sum_isum_j w_j^H Q_ji w_i$. So, by comparing coefficients, we should set $Q_ji=(barh_jh_i^T)otimes(g_jg_i^H)$.
$endgroup$
– user1551
Apr 3 '13 at 20:51
$begingroup$
Let $w_j=operatornamevec(W_j)$. Then $w^T=(w_1^T,ldots,w_n^T)$. Partition $Q$ into subblocks, each of size $ntimes n$. Call the $(j,i)$-th block $Q_ji$. Then by $w^HQw=sum_isum_j w_j^H Q_ji w_i$. So, by comparing coefficients, we should set $Q_ji=(barh_jh_i^T)otimes(g_jg_i^H)$.
$endgroup$
– user1551
Apr 3 '13 at 20:51
|
show 1 more comment
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