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 Feb 1 awarded Notable Question Nov 26 comment How can I immeediately see that the $L_2$ norms of $X^T X$ and $X X^T$ are the same for all real matrices $X$? Your equations are for spectral norm, but my question is about $L_2$ norm (en.wikipedia.org/wiki/Matrix_norm#L2.2C1_norm). $L_2$ norm is not equal to maximum eigenvalue. Nov 21 comment How can I immeediately see that the $L_2$ norms of $X^T X$ and $X X^T$ are the same for all real matrices $X$? @EricTowers That link is about spectral norm, but I am asking about L2 norm. Why is it relevant? Nov 20 comment How can I immeediately see that the $L_2$ norms of $X^T X$ and $X X^T$ are the same for all real matrices $X$? @EricTowers I see, so the L2 norm of a matrix is equal to the L2 norm of vector of its singular values. And the singular values are the same for the two products as can be shown by replacing X by its SVD in the products. Nov 20 asked How can I immeediately see that the $L_2$ norms of $X^T X$ and $X X^T$ are the same for all real matrices $X$? Oct 9 awarded Popular Question Jul 29 revised Concentration inequalities for product of gaussians added 10 characters in body Jul 29 asked Concentration inequalities for product of gaussians Jul 23 comment Find a set of linear equations whose solution is the same as the minimum of a given quadratic objective function @Marconius God, I think you guys are right. It was so simple.. Jul 23 asked Find a set of linear equations whose solution is the same as the minimum of a given quadratic objective function Jul 11 comment Generating a random matrix with all eigenvalues equal to one The reason for orthogonal matrices is computational rather than mathematical. It is much easier to compute transpose than inverse. Jul 11 accepted Generating a random matrix with all eigenvalues equal to one Jul 10 asked Generating a random matrix with all eigenvalues equal to one Jan 29 accepted How to obtain $n$ maximally different binary vectors with equal number of zeros and ones? Jan 7 comment How to obtain $n$ maximally different binary vectors with equal number of zeros and ones? @JorgeFernández The task is to maximize the difference between vectors, not minimize. Jan 7 comment How to obtain $n$ maximally different binary vectors with equal number of zeros and ones? @GerryMyerson Thanks, I added the coding-theory tag. Jan 7 comment How to obtain $n$ maximally different binary vectors with equal number of zeros and ones? @JorgeFernández I don't see it. For example let $m=10$ and $n=5$. Then the smallest $k$ is $11$. Then say we pick the first 11 digits in the vector. Then what do we do? If we select vectors which have all their ones inside those first 11 digits, then all of them will be very close together, but I need them to be far apart. Jan 7 revised How to obtain $n$ maximally different binary vectors with equal number of zeros and ones? edited tags Jan 7 awarded Yearling Jan 7 asked How to obtain $n$ maximally different binary vectors with equal number of zeros and ones?