Fork me on GitHub

Math for the people, by the people.


PlanetMath is a virtual community which aims to help make mathematical knowledge more accessible. PlanetMath's content is created collaboratively: the main feature is the mathematics encyclopedia with entries written and reviewed by members. The entries are contributed under the terms of the Creative Commons By/Share-Alike License in order to preserve the rights of authors, readers and other content creators in a sensible way. We use LaTeX, the lingua franca of the worldwide mathematical community.

Beginning February 23th 2015 we experienced 15 days of downtime when our server stopped working. We moved a backup to DigitalOcean, and we're back online. Some features aren't working yet; we're restoring them ASAP. Please report bugs in the Planetary Bugs Forum or on Github.

User login

Latest Messages  

Another variance and sample size question by jfs 3:27 pm
Hi, I know that the variance halves when the sample size doubles and this makes sense to me when using the variance to compute a confidence interval for the mean. But I presume that relationship doesn't mean that you can adjust data with it? We measure combustions stability in an engine with stdev(IMEP) where IMEP is ~ the average pressure in the cylinder. We normally do stdev(IMEP) over 300 cycles (n = 300). My colleague collected a lot of data with only 100 cycles and has asked me if this can be converted to 300 cycle equivalent. I don't think so but not completely sure about this so would like to ask the maths community? Any help much appreciated.>

[P] sketch proof by akdevaraj 5:12 am
Attention: Pahio and others. Many feel that my terminology is not comprehensible. I therefore propose to develop the sketch proof, step by step, using only commmonly understood terminology. After each step I will give a break for a day. Is this ok?

[P] failure functions - another example by akdevaraj Oct 7
Let our definition of a failure be a non-Carmichael number. Let the parent function be the polynomial f(x) = x^2 + x + 9. When x = 23 we get the Carmichael number 561. However x = 8 + 81k ( k belongs to Z ) is a failure function since when we substitute a value of x generated by this failure function we get only failures ( non-Carmichael numbers ).

[P] Random thoughts on proofs by akdevaraj Oct 6
1) Perhaps some conjectures cannot be proved without collaboration with a programmer - unless the mathematician himself happens to be a gifted programmer 2) What is the value of alternate proofs? For example suppose someone comes up with an alternate proof of Fermat's last theorem - who is going to pay attention even if the latter is simpler?

[P] conjecture - a fewpoints (contd) by akdevaraj Oct 5
3) Bonus: when a value of x, say x', is generated by a failure function we not only know that f(x') is composite- we also know what f(x') is a multiple of. For example let us take the failure function x = 14 + 211k; when k =1, x' = 225. f(14+ 211) is a composite and it is a multiple 211. Needless to say this bonus aspect is not important for application of failure functions in proving the infinitude of primes os shape f(x).

[P] conjecture - a fewpoints by akdevaraj Oct 5
1) I double checked my computations - I am convinced that a value of x, say x', if generated by one or more of the relevant failure functions then f(x') is a failure (composite). If not f(x') is prime and it need not be tested for primality. 2) in the demonstration sample the largest uncovered value of x in the interval chosen is 167; f(167) = 28057 and the second interval to be considered is 167, 28224. Obviously this cannnot be dealt with manually.

[P] conjecture - three points by akdevaraj Oct 3
1) Carl Pomerance has just pointed out an exception to my generalisation.However I stand by my message on x^2 +x +1. 2) A minor correction -second last line - shape 3^q..... (p_(i-1)^z. 3) I ran the program {p(n) = factorint( n^2+n+1) } from n=1 to n=1000. I could not find a single exponent greater than 2.

[P] Conjecture - clarification by akdevaraj Oct 3
Sorry I misunderstood Pomerance; he has clarified that it has not yet been proved.

[P] Conjecture - sketch proof - concluding message by akdevaraj Sep 30
Note 1) p_0 less than p_1 less than p_2........ Hence the intervals get progressively larger; even a small percentage of xs not covered by the relevant failure functions means a sizable number of candidates for initiating the next iteration. However we need only one x not covered by any failure function to go to iteration i + 1. This is the largest of the xs not covered. 2) Only a competent programmer can program the failure functions and perform the iteration. 3) For the sake of demonstration I have selected x = 12 and the interval x = 12, 12 + 157 (12^2 + 12 +1 =157 ). The iteration is done as follows: I make a list of xs starting with 12 and ending with 169. Which are the relevant failure functions? 1+2k, 2 + 7k, 3 + 13k, 4 + 7k, 5 +31k, 6 +43k........ending with 47 + 61k. These are relevant because these cover the interval chosen. Next I circle the xs covered by each failure function. For example 1 + 3k generates 4, 7, 10, ...After performing the same procedure with all the relevant failure functions I found I was left with 37 unmarked xs. The percentage of unmarked xs is 24%. Needless to say f(x), where x is any these 37 is prime. The list of 37 unmarked xs: 14, 15, 17, 20, 24, 27, 33,38, 41, 50...ending with 167. 3) What are the implications of the iteration coming to an end after the ith iteration? p_(i-1) is the largest prime with with shape x^2 + x+1. This means x_(i-1) is the largest uncovered x; all subsequent xs are such that f(x) are composite having shape 3^q7^m13^n.....x_(i-1)^z ( here q,m,n...z are exponents belonging to N). This is highly improbable, perhaps impossible.

[P] Conjecture- sketch proof (contd.) by akdevaraj Sep 29
Briefly the sketch proof consists of the following steps: 1) Iteration: Let p_0 be the largest known prime with shape x^2 + x +1. Let x_0 be the relevant value of x i.e. x_0^2 +x_0 +1 = p_0. Consider the interval x_0, x_0 + p_0.( this interval is chosen because f(x_0 + k*f(x_0)) is congruent to 0 (mod (f(x_0)). ). In each iteration there is a percentage of values of x not covered by the relevant failure functions - these are such that the relevant f(x)s are prime (which need not be tested for primality). Do the relevant failure functions cover the whole interval? If so the iteration has come to an end which means p_0 is the largest prime of the shape x^2 + x + 1 and that there are only a finite number of primes of this shape. If not we go to the second iteration, i_2.: let x_1 be the largest value of x not covered by the relevant failure functions; f(x_1) is prime - let this be p_1. Consider the interval x_1, x_1 + p_1. Do the relevant failure functions cover the this interval completely? If so iteration has come to an end and p_1 is the largest prime of this shape; this also means there are only a finite number of primes of this shape. If not we go to iteration, i_3. My conjecture: the percentage of xs not covered by the relevant failure functions will decrease from iteration to iteration progressively; however the decrease of percentage is asymptotic to 3. i.e. it never reaches 3. Hence the iteration is perpetural. Therefore the infinitude of primes of shape x^2 + x + 1 is proved. (to be continued ).

[P] Conjecture- sketch proof by akdevaraj Sep 29
Conjecture: any irreducible quadratic polynomial, in which the variable belongs to Z, generates an infinite set of prime numbers. For illustration I am taking the irreducible quadratic polynomial: f(x) = x^2+x +1. Definitions:1) failure: a composite number. 2) failure function: x = x_0 + k*x_0 (here a belongs to N and is fixed; k belongs to Z and x_0 is a specific value of x. In other words x is a function of x_0. When we substitute the values of x generated by the failure function in f(x) we get ONLY failures ( composites ). Example: x = 1 +3*k generates 4,7, 10, 13. . . Any of this infinite set, when substituted in f(x) results in a failure (composite). Indirect primality test: in the sketch proof I am developing I will be testing only whether a particular value of x, say x_1, is is covered by one or more failure functions or not. If it is covered, then f(x) is a failure (composite ); otherwise f(x _1) is prime which need not be tested for primality. We do not directly test whether f(x_1) is prime or composite; that is why this is an indirect primality test. (to be continued).

[P] conjecture by akdevaraj Sep 28
Hi, Jussi; Sorry am unable to give the sketch proof without using the mathematical tool viz. "failure functions ".

[P] conjecture by pahio Sep 26
Hi Deva, can you give the proof without failure funtions which ones I don't understand? BTW, see the example Jussi

[P] Conjecture - sketch proof by akdevaraj Sep 26
Before I give the sketch proof I request members to read my article " Failure functions " and the the following message : Application of failure functions - indirect primality test ( both on planetmath ).