1,737 reputation
416
bio website people.su.se/~peal0658
location Sweden
age 27
visits member for 3 years, 11 months
seen Jun 30 at 1:15

Languages: Java, C, C++, Mathematica, Php, HTML, CSS, LaTeX.

Interests in computer science: Fractals, genetic algorithms and AI programming.


Jul
2
awarded  Curious
Jun
13
comment Solving systems of linear congruential equations
See planetmath.org/florentinsmarandache perhaps.
Jun
7
comment On combining $n$ and $n^2$ into one number
@BenjaminDickman: Why discriminate on age? Perhaps it might be suitable for math.stackexchange, but it is seemingly a non-trivial question.
Jun
7
comment Show, by the element method that, for all subsets P, Q, and R of U, (P − Q) ∩ (R − Q) = (P ∩ R) − Q.
Draw a picture. Venn diagrams is your friend. Clarification: This type of problem, can easily be proved using Venn diagrams. Even an elementary picture, can be considered as a proof. In this case, draw 3 circles, as on the wikipedia page, and identify left hand side, and right hand side in the picture. Note that the regions for both "interpretations" are the same.
Jun
7
answered Is $i$ irrational?
Jun
7
comment Number of solutions to sudoku puzzle
@Jeff: General Sudoku ($n^2 \times n^2$ board) is NP-complete. The and the 9x9-board can be reduced to a SAT-problem, so it depends on your efficiency of the SAT-solver. However, this is equivalent to trying to solve the puzzle, I would say. If there was a quick way for 9x9-then most likely, this generalizes to all sizes, and you would become famous/assassinated by CIA.
Jun
7
asked Number of solutions to sudoku puzzle
Jun
1
comment How to evaluate $ \int_{0}^{\frac{\pi}{2}}\frac{1}{(1+x^2)(1+\tan x)}\,\mathrm dx$
I think this is a typo; tan should perhaps be arctan in the question. Then things makes sense.
May
29
comment compact and convex set
How about using weak inequality in your definition, instead of strict? Is that what you mean? What are $X_1,X_2$ and $H$? Vectors?
Mar
22
comment Prove that a point is optimal in LP-problem
Eh, nevermind, found a way to solve the equivalent problem in another way, but it is involved.
Mar
22
awarded  Tumbleweed
Mar
15
asked Prove that a point is optimal in LP-problem
Mar
9
comment Invertibility of NxN nonnegative matrix with diagonally dominant elements
As Benoit tells you; the intuition is as follows; for any such generic matrix, all elements are non-equal. Thus, we may fiddle each element a little bit and still satisfy all conditions you describe. Thus, there is an open ball around each generic matrix. If the generic matrix you started with was non-invertible, then some (most) elements in the small ball around this matrix must be invertible.
Dec
8
answered Circular Permutations With Repetitions (Mirrored Ignored)
Nov
30
comment Fields that require both CS and pure math
Added now, see link.
Nov
30
revised Fields that require both CS and pure math
added link
Nov
13
comment Proving constant function given the second derivative.
Well, since we already assumed that $f' \leq 0$ everywhere, and it is also weakly increasing, so if the limit to the left is 0, then the entire f' is at least 0, but at the same time, it is at most 0. Thus, constant.
Nov
13
comment Proving constant function given the second derivative.
Well, for some $X$, we have that $f'(x)\geq a/2$ if $x>X$, (follows from how limits work). Now, $f$ is just the area under $f'$, from say $X$, plus some constant. But, area under $f'$ from $X$ to infinity is at least the area of a rectangle with height $a/2$ and infinite width, so $f$ must have go to infinity as x does. Or, you can just argue that $f(x)$ must lie above the line $y=ax/2+c$ for some fixed $c$.
Nov
13
answered Proving constant function given the second derivative.
Sep
23
answered How to show that $\cos\frac{2\pi}{n} + \cos\frac{4\pi}{n} + \ldots+ \cos\frac{2\pi(n-1)}{n} = -1$ for all positive integers $n$?