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visits member for 4 years, 4 months
seen Jun 24 '13 at 0:06

No, his mind is not for rent
to any god or government.
Always hopeful, yet discontent.
He knows changes aren't permanent,
but change is.

— Rush, Tom Sawyer


Taking an externally-imposed and much-needed break from SE activities.

E-mail (flipped ROT13): zqd˙ʎʌuzʇ@ʇɐʌǝɥʇʌssqɹǝɥɟuɹʎɔ
Any code I've posted here I place under the WTFPL.


Sep
21
comment Active Contour Models - Lagrangian/Eulerian approches
Mind mentioning where (e.g. book, website) you encountered these?
Sep
21
comment Given coordinates of hypotenuse, how can I calculate coordinates of other vertex?
This is related to the geometric fact that an angle inscribed in a semicircle is a right angle. I suppose there are cases where the algebra with this approach is easier than Robin's, and conversely.
Sep
21
comment Find the range of $x$, given $y_{min} \leq y(x) \leq y_{max}$, where $y(x) $ can be any function ( Updated)
Ah, so it's a rational function! Why didn't you say so to begin with? You can do the analysis by looking at the numerators and denominators; rootfinding of the polynomials in the denominators may sometimes be necessary, but this is certainly more tractable than what you were asking at first.
Sep
21
comment Branches of mathematics not having a general method to solve
Even from the numerics viewpoint, it only takes a tiny change in the initial conditions for some DEs to see a change in the behavior of the solutions. Lorenz's set comes to mind.
Sep
21
comment Find the range of $x$, given $y_{min} \leq y(x) \leq y_{max}$, where $y(x) $ can be any function ( Updated)
As mentioned already, solution strategies for such things are often tailored to the inherent structure of the problem. Not exploiting it can only be a profligate waste of computer time and effort. Please give more specifics about your function(s) of interest. Turning to the multivariate case, exploitation of structure becomes even more important, since you have much degrees of freedom.
Sep
21
comment How to start with mathematics?
Heh, indeed, trying to break your algorithm and trying to poke holes in your proof require the exact same mindset. Building up the discipline to go over such things line-by-line is great practice.
Sep
21
comment Given coordinates of hypotenuse, how can I calculate coordinates of other vertex?
Kevin: mentioning something along the lines of "I tried method X and it went to crap" wouldn't have hurt.
Sep
21
comment Given coordinates of hypotenuse, how can I calculate coordinates of other vertex?
Geometrically, subtracting equation 2 from equation 1 is equivalent to finding the radical line (mathworld.wolfram.com/RadicalLine.html ) of the two circles represented by the two equations.
Sep
21
comment Why does $1/x$ diverge?
This is the Oresme proof, and see math.stackexchange.com/questions/250/840#840 as well for how you might attempt a physical demonstration.
Sep
21
comment How is $\mathbb{C}$ different than $\mathbb{R}^2$?
There's nothing corresponding to "maximum modulus" on $\mathbb{R}^2$.
Sep
21
comment Indirect proof that sum of first n even numbers is $n^2 + n$
...but induction is the most elementary way of going about it, Ignorunt.
Sep
21
answered Indirect proof that sum of first n even numbers is $n^2 + n$
Sep
20
revised Interesting results easily achieved using complex numbers
removed cruft from Amazon link and converted it to a hyperlink
Sep
20
comment Interesting results easily achieved using complex numbers
This is a great example; I remember T mentioning somewhere here that algorithms that have to be restricted to real variables are often clunky compared to algorithms that allow complexes.
Sep
20
comment Branches of mathematics not having a general method to solve
There's still no unified way to represent solutions to transcendental equations in closed form, IIRC.
Sep
20
comment Does a continuous scalar field on a sphere have continuous loop of “isothermic antipodes”
I'd use the word "isothermal" instead.
Sep
20
comment what does ∇ (upside down triangle) symbol mean in this problem
Not that unusual; some optimization books use $\nabla^2$ as shorthand for the Hessian (in the sense of $\nabla$ of $\nabla f$ a.k.a. the gradient).
Sep
20
comment Does a continuous scalar field on a sphere have continuous loop of “isothermic antipodes”
@Rahul: "co-latitude" is "complementary latitude", or ninety degrees minus the latitude. Remember that latitude measures from the x-y plane; co-latitude measures from the z-axis. So what you were supposing is correct.
Sep
20
comment Does a continuous scalar field on a sphere have continuous loop of “isothermic antipodes”
@whuber: Argh, your notation confused me, I use the Greek letters in spherical coordinates the other way around! :D
Sep
20
comment Legendre functions in number theory
Well, you can take derivatives to arbitrary order, remember? ;) Also ${}_2 F_1$ admits an analytic continuation... anyway this is way off what you want; I'll look with interest at what the experts may come up with.