User Qbik - Mathematics Stack Exchange

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	368 reputation	bio	website		visits	member for	1 year, 3 months
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2

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1

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44

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Does $\operatorname{MSE}(\hat{\theta}) = \operatorname{Var}(\theta)+ \left(\operatorname{Bias}(\hat{\theta},\theta)\right)^2$?

may 17 at 10:19 Argha 1,536

1

vote

1

answer

54

views

Is there efficient way of finding last number in following sequence

combinatorics recreational-mathematics

mar 20 at 22:41 YACP 9,220

1

2

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0

answers

27

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For which minimal $k$ true is that ${4}^{k}\cdot n\leq \displaystyle\sum^{n}_{i=1}{a}_{i}^{k}\leq {5}^{k}\cdot n$, ${a}_{i}\in {1,2,3,4,5,6}$?

algebra-precalculus inequality modular-arithmetic recreational-mathematics

mar 19 at 22:47 Qbik 368

0

votes

2

answers

54

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What is sum of occurrences of zeros, at the end of integers, up to number n?

recreational-mathematics

mar 19 at 16:41 Abhijit 1,609

1

2

votes

1

answer

60

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Checking Sudoku - sufficient sums

combinatorics algorithms recreational-mathematics puzzle

mar 14 at 23:01 PyRulez 511

1

vote

3

answers

50

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Are there any Heron-like formulas for convex polygons?

geometry algorithms euclidean-geometry computational-geometry polygons

mar 6 at 2:44 Ron Gordon 26.7k

1

vote

1

answer

37

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Is the Fujiwara bound the most precise bound on maximum absolute value of complex roots of real polynomials?

polynomials complex-numbers roots

feb 25 at 23:12 Antonio Vargas 6,733

1

4

votes

5

answers

184

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What is closed-form expression for $F(n)$ when $F(n)=F(n-1)+F(n-2)$ and $F(0)=a$,$F(1)=b$ and $a,b>0$?

sequences-and-series recurrence-relations recreational-mathematics closed-form

feb 21 at 18:18 André Nicolas 162k

1

vote

1

answer

45

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What is the distribution of empirical covariance between two independent normal distributions?

probability probability-theory probability-distributions normal-distribution convolution

feb 16 at 9:12 Did 103k

0

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1

answer

45

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$u$~$N(0,A)$ and z$|u$~$N(u,1)$ how to show that $u|z$~$N(Bz,B)$ where $B=A/(A+1)$?

probability statistics bayesian

jan 28 at 16:20 Qbik 368

0

votes

1

answer

23

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How to obtain estimate of covariance matrix that will be guarantee to be semi-positive define?

probability matrices soft-question estimation-theory estimation

jan 27 at 21:30 PaulC 26

4

votes

3

answers

123

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Find $C$, if $A=CBC$, where $A$,$B$,$C$ are symmetric matrices.

linear-algebra matrices

jan 24 at 0:49 user1551 16.8k

1

vote

2

answers

105

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What is the sum of $\sum\limits_{i=1}^{n}i^k p^i$?

calculus probability sequences-and-series

aug 8 at 11:22 Norbert 20.8k

1

5

votes

4

answers

322

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What is the sum of $\sum\limits_{i=1}^{n}ip^i$?

calculus sequences-and-series

aug 8 at 13:40 Colonel Panic 187

1

vote

2

answers

37

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What is $f(t)=X_{t+1}$, if $X_{t+1}=(1-p)(1-X_{t})+pX_{t}$ and $X_{0},p \in [0,1]$?

sequences-and-series recurrence-relations

jul 20 at 23:27 André Nicolas 162k

1

vote

1

answer

70

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What is the number of functions $f : A\rightarrow A, \forall_{x\in{A}} f(f(x))=x$, set $A$ have $n$ distinct elements.

combinatorics permutations

may 21 '12 at 18:37 Did 103k

0

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2

answers

104

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Is $M=\{(x,y)\in (0,\infty )\times\mathbb{R} : y=\sin(\frac{1}{x}) \}$ a closed set in space $((0,\infty )\times\mathbb{R} ,\rho_{e})$?

general-topology metric-spaces

may 14 '12 at 19:47 Thomas E. 3,197

5

votes

1

answer

186

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Find all limit points of $M=\left \{ \frac{1}{n}+\frac{1}{m}+\frac{1}{k} : m,n,k \in \mathbb{N} \right \}$ in space $(M,\rho_{e})$

general-topology sequences-and-series limit

may 9 '12 at 13:54 TonyK 11.9k

4

votes

1

answer

79

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Is my proof for $\sum_{i=1}^{n}x_{i}y_{i}\leq \sqrt{\sum_{i=1}^{n}x_{i}^{2}\sum_{i=1}^{n}y_{i}^{2}}$ correct?

inequality induction

may 7 '12 at 16:30 ddd 26

1

vote

1

answer

250

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Proof by induction of triangle inequality in Hilbert space.

inequality induction hilbert-spaces

may 7 '12 at 14:37 Qbik 368

6

votes

4

answers

390

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Is $\pi$ periodic in any numeral system?

number-theory pi number-systems

may 16 at 7:25 wendy.krieger 335

0

votes

0

answers

122

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When is this equation true?

analysis limit

apr 11 '12 at 13:29 Thomas 10.8k

5

votes

2

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117

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Is it equation true - limit

analysis limit

apr 11 '12 at 1:52 Martin Argerami 16.9k

Qbik

23 Questions