<< Chapter < Page Chapter >> Page >

Most of the wide variety of classifiers performed within an order of magnitude of each other, except for one called “Hyperpipes" which performed two orders of magnitude better than any of the others. This struck Dr. Padley as very strange as he had never heard of the Hyperpipes algorithm before.

Current work - elec 631 fall 2011

One interesting aspect of the behavior of the Hyperpipes algorithm on the dataset was the very low true positive rate: less than 10% of the t-tbar events were correctly classified as such. However, the false positive rate was much, much lower – this is what accounted for its good performance. At this point the author became suspicious that the default parameters for the WEKA machine learning algorithms were poorly suited to this application and that some of the other algorithms could also demonstrate greatly improved performance with a little tuning. Since logistic regression is relatively simple, and since the author now understands a little about how the algorithm works from the on-line Stanford course, the decision was made to try and tune it to this application.

Cost matrix

The first stage of tuning involved adjusting the cost matrix. This followed from the observation that when training a classifier, we really want to penalize false positives much more harshly than false negatives. Sacrificing up to 50% of our true positives is acceptable if it leads to a very large decrease in background false positive events and thus an improved signal-to-noise ratio. Keeping the true positive rate relatively high is still important as t-tbar events are rare enough that keeping enough for statistical significance is still a problem, as we shall see a bit later.

A variety of cost matrices were created and the logistic regression classifier in WEKA was trained on a training data set with each one of them. The resulting classification models were then tested on a cross-validation data set. Both the training data set and the cross-validation set had 10,000 of each type of event as before. The results are summarized in Table TODO. Note that as expected, increasing the cost of false positives relative to other kinds of errors greatly improved the signal to noise ratio with an acceptable decrease in the true positive rate. Note that the cost matrices are properly scaled by WEKA: only the relative costs of the different types of errors represented by the cost matrix matter. Interestingly, eliminating the costs associated with misclassifying W background events as QCD background events and vice-versa seems to have no effect on the signal-to-noise ratio.

Choosing a cost matrix which penalizes each type of false positive 300 times more than other types of errors seemed to give good results without leading to diminishing returns in the form of decreased true positives. Penalizing false positives caused by QCD events more than W events didn't improve the results on the large test set.

Ratio of signal to background in training set

Dr. Devika Subramanian of the Rice Computer Science department suggested that classifiers need to be trained on data that has each type of event to be classified in a ratio that is roughly the same as that in the real test data. This suggestion indicated that the previous strategy of training classifiers with an equal ratio of each type of event was unsound. Unfortunately, generating training and test sets with the correct ratio of event types is quite difficult because of the huge backgrounds that must be generated, in this case several million QCD events for every t-tbar event. Generating enough background for 100 t-tbar events would take a modern cpu core over 1000 days to compute enough background.

Questions & Answers

where we get a research paper on Nano chemistry....?
Maira Reply
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
learn
Google
da
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Bhagvanji
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
revolt
da
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
nanocopper obvius
Alexandre
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
Good
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get the best Algebra and trigonometry course in your pocket!





Source:  OpenStax, Introductory survey and applications of machine learning methods. OpenStax CNX. Dec 22, 2011 Download for free at http://legacy.cnx.org/content/col11400/1.1
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Introductory survey and applications of machine learning methods' conversation and receive update notifications?

Ask