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Apr
5
comment How to plot figure on specific time on Matlab
I'm voting to close this question as off-topic because it belongs on Stack Overflow.
Apr
5
comment How to plot figure on specific time on Matlab
Hmm, I just realized this is math.stackexchange - this question should probably be moved to stack overflow
Apr
4
comment Examples of results failing in higher dimensions
Sensitivity to initial conditions, topological mixing and dense periodic orbits.
Jan
5
comment What is the geometric interpretation of the transpose?
@mcb You need to read the rest of the sentence - "can be regarded as a rotation to a new basis, then scaling in this new basis, and finally rotating back to the new basis". The effect of the two rotations cancels out, and the net effect is just a scaling (the magnitudes of the scaling are described by the eigenvalues of the symmetric matrix).
Dec
1
comment Amount become $9$ times in $12$ years at Compound interest. In what time it will become $27$ times
Try taking the square root of both sides.
Oct
12
comment negative number divided by positive number, what would be remainder?
@neolivz4ever But only two where the absolute value of the remainder is less than the divisor - sure, you can write 13 = 1 x 5 + 8 but no one thinks that is a justification for saying that 8 is the remainder after dividing 13 by 5. Look, you have one convention, and almost everyone in the world has a different convention. You can either admit that there are multiple valid conventions, or you can continue to pointlessly insist that you are right and the rest of the world is wrong. There is no interesting discussion to be had in either case.
Oct
10
comment negative number divided by positive number, what would be remainder?
@neolivz4ever As I and many others said, there are multiple conventions on how the quotient is rounded. You are free to use your own convention, but that won't stop other people using a different one!
Jul
10
comment Functions that are their own inversion.
@user121330 Phrases like "it's easy" and "it's trivial" are common mathematical parlance. Like a lot of mathematical language, they have a slightly different meaning to their common English meaning. In particular, when someone describes something as "easy" or "trivial" they often mean that it can be done without introducing significant new ideas, or without requiring a sudden flash of insight. In particular, a calculation or derivation taking many pages of routine algebraic manipulation can be described as "trivial" even though most non-math people would say it is hard.
Feb
9
comment Statistics: Where did this function for normal distribution come from?
They are axioms for the purposes of this answer (i.e. they're assumptions that I am making without any justification). There isn't a name for them that I'm aware of.
Feb
6
comment How to find remainder modulo $n$, when $n$ is a large number
Dear editor - not only did you screw up the math in this post by editing it, you also screwed up the formatting. I have reverted your edit.
Oct
4
comment Choice Problem: choose 5 days in a month, consecutive days are forbidden
Thanks, edited :)
Sep
26
comment Consider the problem minimize $f(x)= x^4 −1. $
The proof of quadratic convergence for Newton's method uses the fact that the first derivative of the function whose zero you are finding (i.e. $f''(x)$ in your case) does not vanish on some interval surrounding the root. But you have $f''(x) = 12x^2$ which is zero at the root $x=0$, so the proof of quadratic convergence fails.
Sep
26
comment Solve linear system with matlab
Also, your text specifies $m\geq n$ but your example has $m < n$ (although I don't think this is relevant - probably just a typo).
Sep
26
comment Solve linear system with matlab
You have more equations than unknowns; why do you expect to be able to find an exact solution?
Sep
11
comment Pseudo Proofs that are intuitively reasonable
@MJD Yes, good to mention the Andreas Blass paper too. I'm not sure whether I knew about it or not when I wrote this answer. If I did, then it was surely an oversight.
Aug
7
comment Coordinate descent with constraints
Thanks Michael!
Aug
6
comment Coordinate descent with constraints
Thanks for this answer Michael. Is it easy to see that when dealing with coordinate-wise bounds, thresholding to $l_i\leq x_i\leq u_i$ at each step results in the global minimizer for the problem I posed (convex function with separable non-smooth constraints and coordinate-wise bounds)?
Aug
1
comment What are some conceptualizations that work in mathematics but are not strictly true?
@BCLC a physicist would say $f(r,\theta)=r^2$ whereas a mathematician would say $f(r,\theta)=r^2+\theta^2$.
Jul
28
comment Interview puzzle with a deck of cards, some cards upside-down
@Wonder Yes, it is the same answer (+1) - I saw that another answer appeared just as I was finishing mine, but since I'd already written it I hit 'post' anyway.
Jul
18
comment What numerical methods are known to solve $L_1$ regularized quadratic programming problems?
I'll certainly give it a shot. I've already tried several general-purpose solvers (open source and commercial) which have been okay, but not as fast as a couple of hand-rolled special-purpose solvers. I've not tried CVX yet though...