Archive for the ‘Math’ Category

The ghost of McNamara is alive and well

Friday, July 10th, 2009

 

Robert McNamara has died.  Unfortunately his brand of social engineering is alive and well.   You may know a couple of Roberts "innovations".  They include the F-111.

 And the ever jamming M-16 rifle.

His life demonstrates the abject failure of when the unwashed hands of government apparatiks touch the inner workings of our society. 

Read George Wills Article to understand better how McNamera introduced his own particular version of errors into the system. 

The apogee of McNamara’s professional life, in the first half of the 1960s, coincided, not coincidentally, with the apogee of the belief that behavioralism had finally made possible a science of politics. Behavioralism held — holds; it is a hardy perennial — that the social and natural sciences are not so different, both being devoted to the discovery of law-like regularities that govern the behavior of atoms, hamsters, humans, whatever.

This sort of social meddling has not ceased.  Unfortunately it has found a new home in the left.  Unable to fathom the mathematics of chaos they straddle the bucking bronco wild horse proclaiming over and over it will end differently this time.  This time we can break this wild horse called human reality.  This from the people who claim there is no god on one hand but on the other purport to have god like qualities of to-the-core understanding.  I think that is unlikely.

I guess all we can do is wait for Obama to be tossed off this pitch black mare with the bewitching eyes.  It will come sure as the sun rises.

 

 

Find the equilateral triangle

Friday, November 21st, 2008

Show that the curve:

x^3 + 3xy + y^3 = 1

contains only one set of three distinct points, A, B, and C, which are vertices of an equilateral triangle, and find its area.

The “curve” x^3+3xy+y^3-1 = 0 is actually reducible, because the left side factors as
(x+y-1)(x^2-xy+y^2+x+y+1 Moreover, the second factor is

{1/2}*((x + 1)^2 + (y + 1)^2 + (x - y)^2) 

so it only vanishes at (-1,-1). Thus the curve in question consists of the single point (-1,-1) together with the line

x + y = 1

To form a triangle with three points on this curve, one of its vertices must be (-1,-1) . The other two vertices lie on the line x + y = 1 so the length of the altitude from (-1,-1) is the distance from (-1,-1) to (1/2,1/2)  or    {3 sqrt{2}}/2  The area of an equilateral triangle of height h is   h^2 sqrt{3}/3   , so the desired area is   {3 sqrt{3}}/2   .

Remark:

The factorization used above is a special case of the fact that

 x^3 + y^3 + z^3-3xyz = (x + y + z)(x + omega y + omega 2z)(x + omega 2y + omega z).

Where omega denotes a primitive cube root of unity. That fact in turn follows from the evaluation of the determinant of the circulant matrix

matrix{3}{3}{x y z z x y y z x }

by reading off the eigenvalues of the eigenvectors (1, omega i, omega 2i) for     i = 0, 1, 2    

Long hand division generation of polynomials

Wednesday, November 12th, 2008

Do a long hand division of 1/{1-x}  

x greater than or equal to 1 does not result in convergence of this sum.  However this algorithm can still be used to do some interesting things.  Let us use a complex value of   x = .707+.707i  

Each power of x yields a result one step around this unit circle. Thus this series is the Z transform of the associated sequence.  [1,0] , [0.707,0.707] , [0,1] ……. This sequence is  Sin( (n-1)*pi/{4})  

Thus the z transform of this sequence is:   1/{1-(0.707+0.707i)*x}    

If you want to get express in terms of n instead of n-1 you can multiply by 1/x.  Since x is the place holder it is easy to see if you want to slide a series one unit to the left by dividing by x. 

 Sin( n*pi/{4})    : note this series starts at 45 degrees phase!

 

More information:

Z transform of and exponentially decaying sequence

Tuesday, November 11th, 2008

The series:   x^n      doubleleftright 1+ x + x^2 + x^3 + ....  = 1/{1-x}    n=0,1,2...   this converges for x < 1 : Both of these expressions are the Z transform of the  x^n   exponential decay sequence.  The first expression is easier to deal with because it is smaller and easier to work with.  The following diagram uses a decay sequence with  x = 0.75 

 

The filter takes what ever input it is fed and every interval multiplies it by 0.75.   To see the filters time response you can thus feed in a single ping.  This results in the filter output tracing out a special response.  This  is called the impulse response. It is the same as the filter plot above.

The exponential decay is maximum entropy.  That is to say this is how concentrated things soak out into the rest of the world as they become more dilute. 

Convolution of time signals using polynomials-The Super Easy Z transform

Tuesday, November 11th, 2008

1+x+x^2 *     1+x+x^2 =   1+2x+3x^2+2x^3+x^4

  • The filter is the sum of the last 3 signal samples. 
  • The signal is a pulse set of three ones.  The signal arrives 1 sample at a time.

Polynomial convolution diagram showing how coefficient of multiplied polynomials correspond to signal amplitudes

Notice the coefficients of the multiplied polynomials are equal to the signal output values at times 0 through 4.

If instead of using X as our variable we could use Z and we would see that all this is the Z transform.   The following principle is true for the above signal and filter.  It is true in general.

    Signal convolved with Filter    doubleleftright Transform of signal *  Transform of filter

Notice that the powers of X perform the function of place holding for location in time.  They keep track of what we can tally and these tallies correspond in power of X to time.  Time=4 corresponds to powers of 4 of X.

Topological Graph Theory References

Saturday, November 8th, 2008

Graph Theory and Its Engineering Applications  By Wai-Kai Chen

Animated Geometric Proof of Pythagoras Theorem using shearing transform

Tuesday, November 4th, 2008

What is most interesting about the following geometric proof is that it uses a shearing transform.  This transform exploits the fact that a parallelogram of equal height and length has equal area.  This gives it a fluid pouring aspect.

Alot of different proofs of Pythagorean theorem.

Two 2 dimensional determinant of a matrix animation showing it is equal to the area of the parallelogram

Tuesday, November 4th, 2008

The 2 dimensional determinant of a matrix can be interpreted as the area of a parallelogram as shown in the following diagram.

This carries on through higher dimensions.  Below depicts a 3 variable system.

The rows r1, r2, r3 are vectors each. The various summations taken 1, 2 and 3 at a time define a parallelepiped. 

 

The following excerpt is from X and may yield some insight when maximum entropy principle is applied. ( still working on this )

 

 

WordPress WP-Latex Plugin for rendering Mathematics

Tuesday, October 28th, 2008

I found another math rendering plugin refered to here: http://www.illigal.uiuc.edu/web/kumara/2007/04/10/latex-math-plugin-for-wordpress/

It is based on LaTeX.

Note To Self:  Kumara Sastry  appears to be an interesting an talented person.  He studies in the area of genetic algorithms.  An idea I have is to study talented people and make a blog and the subsequently a company based around these people. 

Easy LaTeX - author interesting blog to punch around also

I love Miss Loi

Saturday, October 18th, 2008

Saddened by the dismal state of affairs, a sexy shy maths tutor whispered, “Let there be a blog“, and a great math blog was born.

To counter the terrifying disease, she called the math blog Jφss Sticks, and she saw that it was good.

Miss Loi is a Math tutor in Singapore and if  you read much of her writing you can not help but to wish to meet her.

Unfortunately I did not win this contest to visit with her.