Archive for bug
golden bug [jatp]
Posted in pictures, Travel with tags bug, garden, jatp, scarab beetle, summer on August 11, 2021 by xi'angenuine Latinsquare rectangle
Posted in Books, pictures, Statistics, Travel, University life with tags art restoration, bioweapon, bug, Choi Seok-jeong, Firenze, Florence, Italia, latin square, Leonhard Euler, Medicis, NYT, sacrophagus, Serratia ficaria SH7 on June 9, 2021 by xi'an
the strange occurrence of the one bump
Posted in Books, Kids, R, Statistics with tags accept-reject algorithm, bug, code golf, cross validated, debugging, Gamma generator, mixture of distributions, R, sample on June 8, 2020 by xi'anWhen answering an X validated question on running an accept-reject algorithm for the Gamma distribution by using a mixture of Beta and drifted (bt 1) Exponential distributions, I came across the above glitch in the fit of my 10⁷ simulated sample to the target, apparently displaying a wrong proportion of simulations above (or below) one.
a=.9 g<-function(T){ x=rexp(T) v=rt(T,1)<0 x=c(1+x[v],exp(-x/a)[!v]) x[runif(T)<x^a/x/exp(x)/((x>1)*exp(1-x)+a*(x<1)*x^a/x)*a]}
It took me a while to spot the issue, namely that the output of
z=g(T) while(sum(!!z)<T)z=c(z,g(T)) z[1:T]
was favouring simulations from the drifted exponential by truncating. Permuting the elements of z before returning solved the issue (as shown below for a=½)!
weird bug
Posted in Kids, pictures with tags beetle, bug, garden, ladybug, Nezera viridula, raspberries on August 2, 2015 by xi'anLe Monde puzzle [#6]
Posted in R, Statistics with tags bug, Le Monde, mathematical puzzle, prime numbers, schoolmath on February 18, 2011 by xi'anA simple challenge in Le Monde this week: find the group of four primes such that any sum of three terms in the group is prime and the overall sum is minimised. Here is a quick exploration by simulation, using the schoolmath package (with its imperfections):
A=primes(start=1,end=53)[-1] lengthA=length(A) res=4*53 for (t in 1:10^4){ B=sample(A,4,prob=1/(1:lengthA)) sto=is.prim(sum(B[-1])) for (j in 2:4) sto=sto*is.prim(sum(B[-j])) if ((sto)&(sum(B)<res)){ res=sum(B) sol=B} } }
providing the solution 5 7 17 19.
A subsidiary question in the same puzzle is whether or not it is possible to find a group of five primes such that any sum of three terms is still prime. Running the above program with the proper substitutions of 4 by 5 does not produce any solution, even when increasing the upper boundary in A. So it is most likely that the answer is no.