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 Apr 6 comment Why are additional constraint and penalty term equivalent in ridge regression? Can you briefly summarize the paper (since the journal version has some pages)? Apr 6 comment Why are additional constraint and penalty term equivalent in ridge regression? If $\alpha=0$, does it mean the corresponding $c$ can be any non-negative number, according to the second KKT condition? Mar 20 revised How to compute/ find cancellation for the second group cohomology $H^2(G,A)$? Added a missing $in the title Mar 20 suggested approved edit on How to compute/ find cancellation for the second group cohomology$H^2(G,A)$? Jan 27 comment Does Euclidean division not work for general polynomials? ED implies PID. But only polynomials of one variable can form a PID. So no. Dec 9 awarded Excavator Dec 9 revised Does the curvature determine the metric? log -> \log, cos -> \cos, sin -> \sin Dec 9 suggested approved edit on Does the curvature determine the metric? Nov 16 comment How to find$x$such that$\tan5x=\tan x$and$\sin5x=\sin x$? You are welcome :) Nov 16 revised How to find$x$such that$\tan5x=\tan x$and$\sin5x=\sin x$? sin to \sin, x to$x$Nov 16 suggested approved edit on How to find$x$such that$\tan5x=\tan x$and$\sin5x=\sin x$? Nov 16 revised How can I solve this infinite sum? deleted 2 characters in body Nov 15 answered When will$AB=BA$? Sep 24 awarded Autobiographer Aug 12 comment What is the oldest open problem in geometry? I would like to see an animation for a periodic orbit in an obtuse triangle. Jul 24 revised Probability with Uniform Distribution with Multiple Variables texified the body Jul 24 suggested approved edit on Probability with Uniform Distribution with Multiple Variables Jul 11 comment Limit of the integral:$\int_0^{\pi/2}\beta^\alpha\exp\left(-\beta\cos(\theta)\right)d\theta$Shouldn't it be$\lim_{\beta\to+\infty}J_0(\beta)=0$? Illustration. Jul 4 comment 'Obvious' theorems that are actually false You may be interested in these books: Counterexamples in Analysis, Counterexamples in Topology, and Counterexamples in Probability. Jul 2 comment How to prove that:$\tan(3\pi/11) + 4\sin(2\pi/11) = \sqrt{11}$How did you reach the$\sum_i \omega^{2i}=0\$?