642 reputation
310
bio website
location Brooklyn, NY
age 33
visits member for 3 years
seen 14 hours ago
Good Morning how are you, I'm dr jimbob
I'm interested in things.
I'm not a real dr,
But I am a real jim bob.

Have a PhD in Experimental High-Energy Physics, but left academia in mid-2010 to program professionally.

Mostly program/script in python, django, and jquery these days doing mostly web apps.

Also have experience programming in C, C++, java, haskell, php, and (bash) shell more in the past.

Linux as primary OS since 1999, ubuntu user since 2005 (Hoary).


Jun
10
comment 'Obvious' theorems that are actually false
@AnonymousPi $i = \exp\left(\frac{(4n + 1) \pi i}{2}\right)$ where $n \in {\Bbb N}$. Hence $i^i = \exp\left(\frac{-(4n + 1) \pi}{2}\right)$.
Apr
16
awarded  Nice Answer
Oct
9
awarded  Critic
Sep
27
revised Good books and lecture notes about category theory.
fixed link (old link 404s)
Aug
31
awarded  Yearling
Jun
11
awarded  Nice Question
May
23
answered Can we get just $3$ from $\pi$?
May
23
comment Can we get just $3$ from $\pi$?
OP asked: "Without using π again"
May
6
comment Prove $a+b+c+d $ is composite
Note this does not work if you include 0 in the natural numbers. (Obvious counterexample: a = 0, b=3, c=0, d=4, so ab = cd = 0, but a+b+c+d=7 which is prime).
Feb
11
answered 2013th derivative of a trigonometric function
Jan
11
revised How to make two vectors orthogonal?
added 227 characters in body
Jan
11
revised How to make two vectors orthogonal?
Very sloppy bad math on my part.
Jan
11
revised How to make two vectors orthogonal?
added 112 characters in body
Jan
11
answered How to make two vectors orthogonal?
Jan
11
comment How to make two vectors orthogonal?
It's not Gramm-Schmidt. It's Gram-Schmidt (assuming you want to take a set of vectors that spans some space and create a new set of orthogonal vectors - typically also normalized - that spans the same space).
Jan
10
comment How to solve this calculus problem?
@MaoYiyi - There an infinite number of potential functions $f(x)$ that satisfy the given property (e.g., if you assume a form of Ax^4 + Bx^3 + Cx^2 + Dx + E; then A=-134/2475, B = 3622/2475, C=-31924/2475, D=106937/2475, E= -7369/165; or you could assume Ax^10+Bx^8+Cx^6+Dx^4+Ex^2 and get a totally different answer that meets the criteria). E.g., you can give a rough estimate of f'(2.5) based on f(2), f(3) -- even if its more of an average value of f'(x) between 2 and 3.
Jan
10
comment How to solve this calculus problem?
@proximal - I was trying to not suggest evaluate the limit, but to see f'(x) = lim h->0 (f(x+h) - f(x-h))/(2h) we can approximate f'(x) ~ (f(x+h) - f(x-h))/(2h) at several points, exactly as you said. Just was trying to leave it as "hints".
Jan
10
answered How to solve this calculus problem?
Dec
11
comment Does multiplying polynomials ever decrease the number of terms?
Generalizing; let a,b,c,d be non-zero. (x^2 + a x + b)(x^2 + c x + d) = x^4 + (a+c)x^3 + (ac+b+d )x^2 + (ad + bc) + b d. So if a+c = 0, ad + bc + 0, and ac + b+ d = 0 it works. The first eqn gives c = -a; which reduces the second equation to (a)(d-b) = 0, and since a is non-zero means b=d. Hence the last equation becomes 2b - a^2 = 0. So this works for any non-zero a of the form: (x^2 + a x + a^2/2)(x^2 - ax + a^2/2).
Nov
9
comment List of interesting integrals for early calculus students
This is a great integral to show; but not for his purpose without students being exposed to multi-d calculus or being given many hints.