Archive for December, 2007

Euclid’s theorem; p w </math>

Saturday, December 29th, 2007

Euclid’s theorem is generally a reference to the theorem (often credited to Euclid) which demonstrates the existence of an infinite number of prime numbers.

Assume <math>p</math> is the greatest prime number. Let <math>P=\{2,3,5,…,p\}</math> be the set of all prime numbers less than or equal to <math>p</math>, i.e. the set of all primes. Let <math>p’=2\cdot 3\cdot 5\cdot</math> <math> \cdots </math> <math>\cdot p</math> where <math>2,3,5,…,p \in P</math>. It is clear <math>p’</math> is not prime, since every element of <math>P</math> is a factor of <math>p’</math>. Let <math>q=p’+1</math>. Clearly every element of <math>P</math> divides <math>q</math> with a remainder of 1. Thus, <math>q</math> is prime or there exists a prime not in <math>P</math> which divides <math>q</math>. If <math>q</math> is prime, this would contradict our assumption that <math>p</math> is the greatest prime since <math>q>p</math>. Therefore, there must exist a prime that divides <math>q</math> which is not an element of <math>P</math>. But this would contradict our assumption that <math>P</math> is the set of all primes. Contradiction.

Today, Euclid’s result has been strengthened in a number of directions, including Dirichlet’s theorem and the prime number theorem. However, these theorems are significantly more difficult to prove.


External links

  • Euclid’s Theorem at Mathworld

Steven Wallman; prices

Saturday, December 29th, 2007

Steven Wallman was Commissioner of the U.S. Securities and Exchange Commission (SEC) from 1994 to 1997, for which he was appointed by Bill Clinton. He founded FOLIOfn, headquartered in the Tysons Corner, Virginia suburbs of Washington DC in 1998.

In his time with the SEC, he fought for the “decimalization” (i.e. $10.25) of stock prices on the New York Stock Exchange, NASDAQ, and AMEX. Previously, stocks traded in fractions (i.e. $10¼). After much testing and various pilot programs, the first day of decimalized stock prices took place on March 26, 2001.

Biocentric individualism; consume

Saturday, December 29th, 2007

Biocentric Individualism is a system of environmental ethics proposed by noted environmental ethicist Dr. Gary Varner. It is, in part, a revision of the mental state theory of individual welfare, asserting that there is a hierarchy of things of moral importance:

  • Ground project: Things that answer the question “Why is life worth living?” and consume a significant portion of an individual’s life.
  • Non-biological interests: Interests that aren’t as important as ground projects, but more important than mere biological needs.
  • Biological needs: The lowest classification of needs that are still worthy of moral consideration.


See also

  • Maslow’s hierarchy of needs

Operation Währung; those agents

Saturday, December 29th, 2007

During the Battle of the Bulge in WWII, Operation Währung (”Currency” in German) was a special operation conducted as part of Wacht am Rhein.

A small number of German agents infiltrated Allied lines in American uniforms. These agents then used an existing Nazi intelligence network to attempt to bribe rail and port workers to disrupt Allied supply operations.

This operation failed miserably. See Operation Greif.

Life cycle hypothesis; and income

Saturday, December 29th, 2007

The Life Cycle Hypothesis (LCH) is an economic concept analysing individual consumption patterns. It was developed by the economists Irving Fisher, Roy Harrod, Alberto Ando and Franco Modigliani.

Unlike the Keynesian consumption function, which assumes consumption is entirely based on current income, LCH assumes that individuals consume a constant percentage of the present value of their life income.


Literature

  • Robert E. Hall, 1979. Stochastic Implications of the Life Cycle-Permanent Income Hypothesis: Theory and Evidence, NBER


See also

Permanent income hypothesis

Escape fire; consume

Saturday, December 29th, 2007

An escape fire is a fire lit to clear an area of vegetation in the face of an approaching wildfire when no escape exists. Unlike backfires, escape fires are not attempts to control – let alone stop – a wildfire.

The technique had been described in James Fenimore Cooper’s 1827 novel The Prairie but became well-known only after the Mann Gulch fire. On this occasion, Wagner Dodge came up with the same idea independently, and successfully put it into practice. He cleared an area large enough for him to survive unharmed when the main fire was less than one minute away.

Escape fires are an option in grassland but do not work in forest fires because timber burns too slowly to consume the fuel before the main fire arrives.

Gold gram; prices

Saturday, December 29th, 2007

A gold gram is the amount of value represented by exactly one gram of gold. It is a unit of account frequently used for digital gold currencies. It is sometimes denoted by the symbol “gg”, “AUG”, or “GAU”.

A milligram of gold is sometimes referred to as a mil or mgg. Therefore, 1 AUG = 1 gg = 1000 mgg = 1000 mil, and 1 mil = 1 mgg = 0.001 gg = 0.001 AUG. This allows gold holdings and transfers to take place in tiny fractions of a gram (equivalent to a few cents)

A possible source of confusion is that gold is often priced on the open market in the more traditional troy ounce (one troy ounce is exactly 31.1034768 grams, which is larger than the avoirdupois ounce generally in use in the United States and has a mass of 28.35 grams). Some services such as BullionVault use kilogram prices of gold, with the smallest denomination being 0.001 kg or 1 g (equivalent to approximately $21.50 as of May 2007). Kilogram gold prices are also commonly used by the Zurich Gold Pool, where 1,000 kilograms = one metric tonne.


See also

  • Digital gold currency
  • Digital currency exchanger
  • Gold standard


External links

  • Prices of Gold Grams in various fiat currencies

CMS Energy; the natural utilities favored

Saturday, December 29th, 2007

CMS Energy is a public utility supplying electric power and natural gas to most of Michigan. Its headquarters are located in Jackson, Michigan. The company has operated since 1890.

Its two principal subsidiaries are Consumers Energy and CMS Enterprises. Consumers Energy is a public utility that provides natural gas and electricity to more than 6 million of Michigan’s 10 million residents and serves customers in all 68 of the state’s Lower Peninsula counties. CMS Enterprises’ primary businesses are independent power production and natural gas transmission.

The company’s trademark slogan as of 2003 is “Count on Us”.

CMS Energy is also known as CMS, and is listed on the NYSE as . CMS Energy is a member of the S&P 500 and the Fortune 1000.

See also: Lists of public utilities


External links

  • Official CMS Energy site

Margarita Galinovskaya; faced

Saturday, December 29th, 2007

Margarita Galinovskaya (born 19 April 1968) is a Russian competitor in archery.

Galinovskaya represented Russia at the 2004 Summer Olympics. She placed 15th in the women’s individual ranking round with a 72-arrow score of 639. In the first round of elimination, she faced 40th-ranked fellow Russian Elena Dostay. Galinovskaya defeated Dostay 153-136 in the 18-arrow match to advance to the round of 32. In that round, she faced 18th-ranked German archer Cornelia Pfohl. Galinovskaya won the match 158-156 in the regulation 18 arrows, advancing to the round of 16. She then lost to 2nd-ranked and eventual silver medalist Lee Sung Jin of Korea 165-163, finishing 12th in women’s individual archery.

Galinovskaya was also a member of the 9th-place Russian women’s archery team.

CRSP; prices

Saturday, December 29th, 2007

CRSP can refer to:

  • Barnabite, a religious order
  • Center for Research in Security Prices at the University of Chicago
  • Colorado River Storage Project

Prime constant; w </math>

Saturday, December 29th, 2007

The prime constant is the number <math>\rho</math> whose <math>n</math>th binary digit is 1 if <math>n</math> is prime and 0 if it is composite.

In other words, <math>\rho</math> is simply the number whose binary expansion corresponds to the indicator function of the set of prime numbers. That is,

<math> \rho = \sum_{p} \frac{1}{2^p} = \sum_{n=1}^\infty \frac{\chi_{\mathbb{P}}(n)}{2^n}</math>

where <math>p</math> indicates a prime and <math>\chi_{\mathbb{P}}</math> is the characteristic function of the primes.

The beginning of the decimal expansion of ρ is: <math> \rho = 0.414682509851111660248109622… </math>


Irrationality

The number <math>\rho</math> is easily shown to be irrational. To see why, suppose it were rational.

Denote the <math>k</math>th digit of the binary expansion of <math>\rho</math> by <math>r_k</math>. Then, since <math>\rho</math> is assumed rational, there must exist <math>N</math>, <math>k</math> positive integers such that
<math>r_n=r_{n+ik}</math> for all <math>n > N</math> and all <math>i \in \mathbb{N}</math>.

Since there are an infinite number of primes, we may choose a prime <math>p > N</math>. By definition we see that <math>r_p=1</math>. As noted, we have <math>r_p=r_{p+ik}</math> for all <math>i \in \mathbb{N}</math>. Now consider the case <math>i=p</math>. We have <math>r_{p+i \cdot k}=r_{p+p \cdot k}=r_{p(k+1)}=0</math>, since <math>p(k+1)</math> is composite because <math>k+1 \geq 2</math>. Since <math>r_p \neq r_{p(k+1)}</math> we see that <math>\rho</math> is irrational.

(p,q) shuffle; p w </math>

Saturday, December 29th, 2007

Let <math>p</math> and <math>q</math> be positive natural numbers. Further, let <math>S(k)</math> be the set of permutations of the numbers <math>\{1,\ldots, k\}</math>. A permutation <math>\tau</math> in <math>S(p+q)</math> is a (p,q)shuffle if

<math> \tau(1) < \cdots < \tau(p) \,</math>,
<math> \tau(p+1) < \cdots < \tau(p+q) \,</math>.

The set of all <math>(p,q) </math> shuffles is denoted by <math>S(p,q).</math>

It is clear that

<math>S(p,q)\subset S(p+q).</math>

Since a <math>(p,q) </math> shuffle is completely determined by how the <math>p</math> first elements are mapped, the cardinality of <math>S(p,q)</math> is

<math>{p+q \choose p}.</math>

The wedge product of a <math>p</math>-form and a <math>q</math>-form can be defined as a sum over <math>(p,q) </math> shuffles.


Expenditure function; utility

Saturday, December 29th, 2007

In microeconomics, the expenditure function describes the minimum amount of money an individual needs to achieve some level of utility, given a utility function and prices.

Formally, if there is a utility function <math>u</math> that describes preferences over L commodities, the expenditure function

<math>e(p, u^*) : \textbf R^L_+ \times \textbf R
\rightarrow \textbf R</math>

says what amount of money is needed to achieve a utility <math>u^*</math> if prices are set by <math>p</math>.
This function is defined by

<math>e(p, u^*) = \min_{x \in \geq(u^*)} p \cdot x</math>

where

<math>\geq(u^*) = \{x \in \textbf R^L_+ : u(x) \geq u^*\}</math>

is the set of all packages that give utility at least as good as <math>u^*</math>.


See also

  • Expenditure minimization problem
  • Hicksian demand function
  • Utility maximization problem
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David Ludwig; consume

Friday, December 28th, 2007
For the composer, see David Ludwig (composer).
For the convicted murderer, see David G. Ludwig.

In 2000, Dr. David Ludwig, the Director of the Obesity Program at the Children’s Hospital Boston, studied the effects of consuming soft drinks on childhood obesity. Through extensive studies, he showed that the chances of becoming obese increased by approximately 60% for each daily soda the child consumed. He also showed that school children who consume at least 8 ounces of soft drinks daily consume about 835 calories more than children who avoid soft drinks. Ludwig published his findings in The Lancet.


See also

  • Hereditary factors in childhood obesity


External links

  • An article on obesity and soft drinks by Dr. Ludwig
  • Children’s Hospital Internal Page for Dr. Ludwig

Sign test; computed from

Friday, December 28th, 2007

In statistics, the sign test can be used to test the hypothesis that there is “no difference” between the continuous distributions of two random variables X and Y. Formally:

Let p = Pr(X > Y), and then test the null hypothesis H0: p = 0.50. This hypothesis implies that given a random pair of measurements (xi, yi), then xi and yi are equally likely to be larger than the other.

Independent pairs of sample data are collected from the populations {(x1, y1), (x2, y2), . . ., (xn, yn)}. Pairs are omitted for which there is no difference so that there is a possibility of a reduced sample of m pairs.

Then let w be the number of pairs for which yi − xi > 0. Assuming that H0 is true, then W follows a binomial distribution W ~ b(m, 0.5).

The left-tail value is computed by Pr(Ww), which is the p-value for the alternative H1: p < 0.50. This alternative means that the X measurements tend to be higher.

The right-tail value is computed by Pr(Bw), which is the p-value for the alternative H1: p > 0.50. This alternative means that the Y measurements tend to be higher.

For a two-sided alternative H1 the p-value is twice the smallest tail-value.


References

  • Abdi, H. (2007).[1] Binomial Distribution: Binomial and Sign Tests. In N.J. Salkind (Ed.): Encyclopedia of Measurement and Statistics. Thousand Oaks (CA): Sage.

Risk-utility test; utility

Friday, December 28th, 2007

In legal disputes regarding product liability, a risk-utility test is used to determine whether a product’s design or warning is defective, thereby making the manufacturer liable for injuries caused by its product.

The manufacturer is held liable under the risk-utility test if the probability of injury times the gravity of injury under the current product design is more than the cost of an alternative reasonable design plus the diminished utility resulting from modifying the design. More simply, the court considers if the economic costs (determined from likely lawsuits) are higher than the cost of changing the product design (ex: installing a plastic guard) plus the loss of use of the product (ex: the new guard makes it harder to use the product).

HDD Utility Disc; optimal utility

Friday, December 28th, 2007

HDD Utility Disc is software to format a hard disk drive for use in a PlayStation 2 console. It only works with the official PlayStation 2 HDD unit. It makes the HDD appear in the PlayStation 2 Browser on the same screen that game discs, video DVDs, music CDs, and Memory Cards appear.

HDD Utility Disc’s main feature is to allow creation of folders on the HDD to store game save files. If a folder named “Your Saves” is present on the HDD, games that support saving to the HDD and loading from it will use that folder. If that folder doesn’t exist, the games will create it when attempting to save to the HDD. It should be noted that while quite a few Japanese PlayStation 2 games support the HDD as a location to save and load game saves, support for that function of the HDD, and many others, were removed from nearly every North American release of those games during the time before the North American HDD release (ex. Xenosaga Episode 1, Dark Cloud 2, Kingdom Hearts, Final Fantasy X), and even a few games afterwards (ex. Star Ocean: Till the End of Time Director’s Cut).

The only other feature of HDD Utility Disc is enabling launching of games installed to the HDD, though it can only do so if the game supports launching from the HDD, and most games that install to the HDD require being launched from the original disc as an anti-piracy measure.

HDD Utility Disc 1.00 was included with Japanese HDD units from mid-2001, when the HDD launched in Japan, until early 2002, when PlayStation Broadband Navigator replaced it.

HDD Utility Disc 1.01 was included with North American HDD units, which were released on March 23, 2004 as the Final Fantasy XI / HDD bundle, instead of North America getting a release of the current version of the PlayStation Broadband Navigator software. There appears to be no difference in functions between versions 1.00 and 1.01 of HDD Utility Disc.

Due to the HDD not being released in PAL regions, except in Linux Kits, there exists no version of HDD Utility Disc for PAL PlayStation 2 consoles.

Utility vault; utility

Friday, December 28th, 2007

A utility vault is an underground room providing access to subterranean public utility equipment, such as valves for water or natural gas pipes, or switchgear for electrical or telecommunications equipment.

Utility vaults are commonly constructed out of reinforced concrete boxes, poured cement or brick. Small ones are usually entered through a manhole or grate on the topside. Such vaults are considered confined spaces and can be hazardous to enter. Large utility vaults are similar to mechanical or electrical rooms in design and content.


External link

  • National Precast Concrete Association

EBITA; income

Friday, December 28th, 2007

EBITA is an acronym that refers to a company’s earnings before the deduction of interest, tax and amortization expenses. See EBITDA. It is a financial indicator used widely as a measure of efficiency and profitability. EBITA margins in developing telecom markets can be as high as 60%, but margins vary greatly across industries and over time.

EBITA can be calculated by taking the Profit Before Taxation (PBT/EBT) figure as shown on the Consolidated Income Statement, and adding back Net Interest and Amortization. Often, Amortization charges are zero and therefore EBIT = EBITA.

Linear approximation; function <math>v

Thursday, December 27th, 2007


In mathematics, a linear approximation is an approximation of a general function using a linear function (more precisely, an affine function).

For example, given a differentiable function f of one real variable, Taylor’s theorem for n=1 states that

<math> f(x) = f(a) + f\ ‘(a)(x - a) + R_2 </math>

where <math>R_2</math> is the remainder term. The linear approximation is obtained by dropping the remainder:

<math> f(x) \approx f(a) + f\ ‘(a)(x - a)</math>

which is true for x close to a. The expression on the right-hand side is just the equation for the tangent line to the graph of f at (a, f(a)), and for this reason, this process is also called the tangent line approximation.

One can also use linear approximations for vector functions of a vector variable, in which case the derivative at a point is replaced by the Jacobian matrix. For example, given a differentiable function <math>f(x, y)</math> with real values, one can approximate <math>f(x, y)</math> for <math>(x, y)</math> close to <math>(a, b)</math> by the formula

<math>f\left(x,y\right)\approx f\left(a,b\right)+\frac{\partial f}{\partial x}\left(a,b\right)\left(x-a\right)+\frac{\partial f}{\partial y}\left(a,b\right)\left(y-b\right).</math>

The right-hand side is the equation of the plane tangent to the graph of <math>z=f(x, y)</math> at <math>(a, b).</math>

In the more general case of Banach spaces, one has

<math> f(x) \approx f(a) + Df(a)(x - a)</math>

where <math>Df(a)</math> is the Fréchet derivative of <math>f</math> at <math>a</math>.


Examples

To find an approximation of <math>\sqrt[3]{25}</math> one can do as follows.

  1. Consider the function <math> f(x)= x^{1/3}.\,</math> Hence, the problem is reduced to finding the value of <math>f(25)</math>.
  2. We have
    <math> f\ ‘(x)= 1/3x^{-2/3}.</math>
  3. According to linear approximation
    <math> f(25) \approx f(27) + f\ ‘(27)(25 - 27) = 3 - 2/27.</math>
  4. The result, 2.926, lies fairly close to the actual value 2.924…

Copyright laws in Greece; consume

Thursday, December 27th, 2007

The copyright laws in Greece are part of the frame of laws which are constantly being adapted to the guidelines of the European Union.

The enforcement of the copyright laws varies from case to case. Greece has attracted attention because of its extended software and music piracy. The Greek government has tried to impose countermeasures such as the prosecution of those who produce or consume pirated material, with questionable results.

OpenGL Utility Library; utility

Thursday, December 27th, 2007

The OpenGL Utility Library (GLU) is a computer graphics library.

It consists of a number of functions that use the base OpenGL library to provide higher-level drawing routines from the more primitive routines that OpenGL provides. It is usually distributed with the base OpenGL package.

Among these features are mapping between screen- and world-coordinates, generation of texture mipmaps, drawing of quadric surfaces, NURBS, tessellation of polygonal primitives, interpretation of OpenGL error codes, an extended range of transformation routines for setting up viewing volumes and simple positioning of the camera, generally in more human-friendly terms than the routines presented by OpenGL. It also provides additional primitives for use in OpenGL applications, including spheres, cylinders and disks.

GLU functions can be easily recognized by looking at them because they all have glu as a prefix. An example function is gluOrtho2D() which defines a two dimensional orthographic projection matrix.

Specifications for GLU are available at the
OpenGL specification page


See also

  • OpenGL Utility Toolkit (GLUT)
  • OpenGL User Interface Library (GLUI)

Illustration of the central limit theorem; qualitatively the

Thursday, December 27th, 2007

Here is a static illustration of the central limit theorem (you can also see the dynamic SOCR CLT Activity).
A probability density function is shown in the first figure.
Then the densities of the sums of two, three, and four independent identically distributed variables, each having the original density, are shown in the following figures.
Although the original density is far from normal,
the density of the sum of just a few variables with that density is much smoother and has some of the qualitative features of the normal density.

A more concrete illustration, in which most of the arithmetic can be done more-or-less instantly by hand, is at concrete illustration of the central limit theorem. There is also a free full-featured interactive simulation available which allows you to set up various distributions and adjust the sampling parameters (see “external links” at the bottom of this page).

Contents


Density of a sum of random variables

The density of the sum of two independent real-valued random variables equals the convolution of the density functions of the original variables.

Thus, the density of the sum of m+n terms of a sequence of independent identically distributed variables equals the convolution of the densities of the sums of m terms and of n term.
In particular, the density of the sum of n+1 terms equals the convolution of the density of the sum of n terms with the original density (the “sum” of 1 term).

If the original density is a piecewise polynomial, then so are the sum densities, of increasingly higher degree.


The example

The convolutions were computed via the discrete Fourier transform.
A list of values y = f(x0 + k Δx) was constructed, where f is the original density function, and Δx is approximately equal to 0.002, and k is equal to 0 through 1000.
The discrete Fourier transform Y of y was computed.
Then the convolution of f with itself is proportional to the inverse
discrete Fourier transform of the pointwise product of Y with itself.


Original density function

We start with a probability density function. This function, although discontinuous, is far from the most pathological example that could be created. It is a piecewise polynomial, with pieces of degrees 0 and 1. The mean of this distribution is 0 and its standard deviation is 1.


Sum of two terms

Next we compute the density of the sum of two independent variables, each having the above density.
The density of the sum is the convolution of the above density with itself.

The sum of two variables has mean 0.
The density shown in the figure at right has been rescaled by √2, so that its standard deviation is 1.

This density is already smoother than the original.
There are obvious lumps, which correspond to the intervals on which the original density was defined.


Sum of three terms

We then compute the density of the sum of three independent variables, each having the above density.
The density of the sum is the convolution of the first density with the second.

The sum of three variables has mean 0.
The density shown in the figure at right has been rescaled by √3, so that its standard deviation is 1.

This density is even smoother than the preceding one.
The lumps can hardly be detected in this figure.


Sum of four terms

Finally, we compute the density of the sum of four independent variables, each having the above density.
The density of the sum is the convolution of the first density with the third.

The sum of four variables has mean 0.
The density shown in the figure at right has been rescaled by √4, so that its standard deviation is 1.

This density appears qualitatively very similar to a normal density.
No lumps can be distinguished by the eye.


External links

  • General Dynamic SOCR CLT Activity
  • Interactive Simulation of the Central Limit Theorem for Windows
  • Java applet demonstrating the Central Limit Theorem with rolls of dice