I'm trying to train a classifier to detect a fall based on accelerometer and gyroscope data. However, I'm having a hard time determining what type of algorithm to use.
This is a picture of some of the dataset:
This data is an example of raw x-,y- and z-coordinates read from the accelerometer during a fall. As you can see, the data is relatively steady until the point where the fall begins.
My question is: what classifier should I use to detect the fall.
I've read some research in the field, where the scientists used Naive-Bayes algorithms to classify the data, but as I understand it, Naive-Bayes doesn't take into account the previous datasets in the classification.
I thought about using an HMM, but since I'm quite new to machine learning, I thought I'd ask for some general guidance.
Thanks in advance.
You should look at Conditional Random Field (CRF) which can be used as a classifier to take "neighboring samples" into account. If you do some google search, you should be able to find some papers about "fall detection" with CRF.
As you mentioned, HMM is also an appropriate model for your problem, in which you have a hidden variable (fall or not) but unobservable (only x-y-z coordinates are observable).
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The problem is as follows:
I want to use a forecasting algorithm to predict heat demand of a not further specified household during the next 24 hours with a time resolution of only a few minutes within the next three or four hours and lower resolution within the following hours.
The algorithm should be adaptive and learn over time. I do not have much historic data since in the beginning I want the algorithm to be able to be used in different occasions. I only have very basic input like the assumed yearly heat demand and current outside temperature and time to begin with. So, it will be quite general and unprecise at the beginning but learn from its Errors over time.
The algorithm is asked to be implemented in Matlab if possible.
Does anyone know an apporach or an algortihm designed to predict sensible values after a short time by learning and adapting to current incoming data?
Well, this question is quite broad as essentially any algorithm for forcasting or data assimilation could do this task in principle.
The classic approach I would look into first would be Kalman filtering, which is a quite general approach at least once its generalizations to ensemble Filters etc. are taken into account (This is also implementable in MATLAB easily).
https://en.wikipedia.org/wiki/Kalman_filter
However the more important part than the actual inference algorithm is typically the design of the model you fit to your data. For your scenario you could start with a simple prediction from past values and add daily rhythms, influences of outside temperature etc. The more (correct) information you put into your model a priori the better your model should be at prediction.
For the full mathematical analysis of this type of problem I can recommend this book: https://doi.org/10.1017/CBO9781107706804
In order to turn this into a calibration problem, we need:
a model that predicts the heat demand depending on inputs and parameters,
observations of the heat demand.
Calibrating this model means tuning the parameters so that the model best predicts the heat demand.
If you go for Python, I suggest to use OpenTURNS, which provides several data assimilation methods, e.g. Kalman filtering (also called BLUE):
https://openturns.github.io/openturns/latest/user_manual/calibration.html
I have to implement, as part of an assignment, a learning method that enables minesweepers to avoid colliding with mines. I have been given the choice to choose between a supervised/unsupervised/reinforcement learning algorithm.
I remember in one of my lectures, the lecturer mentioned ALVIN. He was teaching artificial neural networks.
Since the behaviour I'm looking for is more or less similar to ALVINN's, I want to implement an ANN. I've implemented an ANN before for solving the 3-parity xor problem, here's my solution. I've never really understood the intuition behind ANNs.
I was wondering, what could the inputs be to my ANN? In the case of the 3parity xor problem it was obvious.
When it comes to frameworks for ANN, each person will have their own preferences. I recently used Encog framework for implementing an image processing project and found it very easy to implement.
Now, coming to your problem statement, "a learning method that enables minesweepers to avoid colliding with mines" is a very wide scope. What is indeed going to be your input to the ANN? You will have to decide your input based on whether it is going to be implemented on a real robot or in a simulation environment.
It can be clearly inferred that an unsupervised learning can be ruled out if you are trying to implement something like the ALVIN.
In a simulation environment, the best option is if you can somehow form a grid map of the environment based on the simulated sensor data. Then the occupancy grid surrounding the robot can form a good input to the robot's ANN.
If you can't form a grid map (if the data is insufficient), then you should try to feed all the available and relevant sensor data to the ANN. However, they might have to be pre-processed, depending on the modelled sensor noise given by your simulation environment. If you have a camera feed (like the ALVIN model), then you may directly follow their footsteps and train your ANN likewise.
If this is a real robot, then the choices vary considerably, depending upon the robustness and accuracy requirements. I really hope you do not want to build a robust and field-ready minesweeper single-handedly. :) For a small, controlled environment, your options will be very similar to that of a simulated environment, however sensor noise would be nastier and you would have to figure in various special cases into your mission planner. Still, it would be advisable to fuse a few other sensors (LRF, ultrasound etc.) with vision sensors and use it as an input to your planner. If nothing else is available, copy paste the ALVIN system with only a front camera input.
The ANN training methodology will be similar (if using only vision). The output will be right/left/straight etc. Try with 5-7 hidden layer nodes first, since that is what ALVIN uses. Increase it up to 8-10 max. Should work. Use activation functions properly.
Given its success in the real world, ALVIN seems like a good system to base yours off of! As the page you linked to discusses, ALVIN essentially receives an image of the road ahead as its input. On a low level, this is achieved through 960 input nodes representing a 30X32 pixel image. The input value for each node is the color saturation of the pixel that that node represents (with 0 being a completely white image and 1 being a completely black image, or something along those lines) (I'm pretty sure the picture is greyscale, although maybe they're using color now, which could be achieved, for instance, by using three input nodes per pixel, one representing red saturation, one representing green, and one blue). Is there a reason that you don't think that this would be a good input for your system too?
For more low level details, see the original paper.
I am looking for a way to combine data from a compass and gyro in order to determine attitude after the fact. I will be working with a complete data set in which the 3D compass and gyro readings have been recorded at regular intervals, but I want to recover an estimate of attitude in post-processing.
I've considered simply using a Kalman filter, since they are so well documented, but would rather use something more appropriate to a case where the complete data set is known. I have a feeling the solution is "simply" a least squares problem, but I'm hoping someone here can point me in the direction of a paper or two dealing with this problem (or problems like it).
At this point, I'm not even sure what this filter would be called, so I'm having a hard time finding useful search terms. Any help would be appreciated.
Thanks so much!
If you understand the Kalman filter in details, you can also implement the so-called Kalman smoother which operates on the complete data set.
However, let me warn you about one thing. There is no such thing as Kalman Filter for programmers. Kalman filter is difficult to understand. You won't be able to implement and use it correctly if you do not understand it.
My implementation is almost what you are looking for. I used accelerometer and gyroscopes but no compasses. It is based on this manuscript, read it first. The most detailed description I have at the moment is slides 29-32 in my presentation on sensor fusion. It is an open source project, and I plan to release an updated version of the solver in the upcoming weeks.
If I have a large set of data that describes physical 'things', how could I go about measuring how well that data fits the 'things' that it is supposed to represent?
An example would be if I have a crate holding 12 widgets, and I know each widget weighs 1 lb, there should be some data quality 'check' making sure the case weighs 13 lbs maybe.
Another example would be that if I have a lamp and an image representing that lamp, it should look like a lamp. Perhaps the image dimensions should have the same ratio of the lamp dimensions.
With the exception of images, my data is 99% text (which includes height, width, color...).
I've studied AI in school, but have done very little outside of that.
Are standard AI techniques the way to go? If so, how do I map a problem to an algorithm?
Are some languages easier at this than others? Do they have better libraries?
thanks.
Your question is somewhat open-ended, but it sounds like you want is what is known as a "classifier" in the field of machine learning.
In general, a classifier takes a piece of input and "classifies" it, ie: determines a category for the object. Many classifiers provide a probability with this determination, and some may even return multiple categories with probabilities on each.
Some examples of classifiers are bayes nets, neural nets, decision lists, and decision trees. Bayes nets are often used for spam classification. Emails are classified as either "spam" or "not spam" with a probability.
For you question you'd want to classify your objects as "high quality" or "not high quality".
The first thing you'll need is a bunch of training data. That is, a set of objects where you already know the correct classification. One way to obtain this could be to get a bunch of objects and classify them by hand. If there are too many objects for one person to classify you could feed them to Mechanical Turk.
Once you have your training data you'd then build your classifier. You'll need to figure out what attributes are important to your classification. You'll probably need to do some experimentation to see what works well. You then have your classifier learn from your training data.
One approach that's often used for testing is to split your training data into two sets. Train your classifier using one of the subsets, and then see how well it classifies the other (usually smaller) subset.
AI is one path, natural intelligence is another.
Your challenge is a perfect match to Amazon's Mechanical Turk. Divvy your data space up into extremely small verifiable atoms and assign them as HITs on Mechanical Turk. Have some overlap to give yourself a sense of HIT answer consistency.
There was a shop with a boatload of component CAD drawings that needed to be grouped by similarity. They broke it up and set it loose on Mechanical Turk to very satisfying results. I could google for hours and not find that link again.
See here for a related forum post.
This is a tough answer. For example, what defines a lamp? I could google images a picture of some crazy looking lamps. Or even, look up the definition of a lamp (http://dictionary.reference.com/dic?q=lamp). Theres no physical requirements of what a lamp must look like. Thats the crux of the AI problem.
As for data, you could setup Unit testing on the project to ensure that 12 widget() weighs less than 13 lbs in the widetBox(). Regardless, you need to have the data at hand to be able to test things like that.
I hope i was able to answer your question somewhat. Its a bit vauge, and my answers are broad, but hopefully it'll at least send you in a good direction.
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How can the tempo/BPM of a song be determined programmatically? What algorithms are commonly used, and what considerations must be made?
This is challenging to explain in a single StackOverflow post. In general, the simplest beat-detection algorithms work by locating peaks in sound energy, which is easy to detect. More sophisticated methods use comb filters and other statistical/waveform methods. For a detailed explication including code samples, check this GameDev article out.
The keywords to search for are "Beat Detection", "Beat Tracking" and "Music Information Retrieval". There is lots of information here: http://www.music-ir.org/
There is a (maybe) annual contest called MIREX where different algorithms are tested on their beat detection performance.
http://nema.lis.illinois.edu/nema_out/mirex2010/results/abt/mck/
That should give you a list of algorithms to test.
A classic algorithm is Beatroot (google it), which is nice and easy to understand. It works like this:
Short-time FFT the music to get a sonogram.
Sum the increases in magnitude over all frequencies for each time step (ignore the decreases). This gives you a 1D time-varying function called the "spectral flux".
Find the peaks using any old peak detection algorithm. These are called "onsets" and correspond to the start of sounds in the music (starts of notes, drum hits, etc).
Construct a histogram of inter-onset-intervals (IOIs). This can be used to find likely tempos.
Initialise a set of "agents" or "hypotheses" for the beat-tracking result. Feed these agents the onsets one at a time in order. Each agent tracks the list of onsets that are also beats, and the current tempo estimate. The agents can either accept the onsets, if they fit closely with their last tracked beat and tempo, ignore them if they are wildly different, or spawn a new agent if they are in-between. Not every beat requires an onset - agents can interpolate.
Each agent is given a score according to how neat its hypothesis is - if all its beat onsets are loud it gets a higher score. If they are all regular it gets a higher score.
The highest scoring agent is the answer.
Downsides to this algorithm in my experience:
The peak-detection is rather ad-hoc and sensitive to threshold parameters and whatnot.
Some music doesn't have obvious onsets on the beats. Obviously it won't work with those.
Difficult to know how to resolve the 60bpm-vs-120bpm issue, especially with live tracking!
Throws away a lot of information by only using a 1D spectral flux. I reckon you can do much better by having a few band-limited spectral fluxes (and maybe one broadband one for drums).
Here is a demo of a live version of this algorithm, showing the spectral flux (black line at the bottom) and onsets (green circles). It's worth considering the fact that the beat is extracted from only the green circles. I've played back the onsets just as clicks, and to be honest I don't think I could hear the beat from them, so in some ways this algorithm is better than people at beat detection. I think the reduction to such a low-dimensional signal is its weak step though.
Annoyingly I did find a very good site with many algorithms and code for beat detection a few years ago. I've totally failed to refind it though.
Edit: Found it!
Here are some great links that should get you started:
http://marsyasweb.appspot.com/
http://www.vamp-plugins.org/download.html
Beat extraction involves the identification of cognitive metric structures in music. Very often these do not correspond to physical sound energy - for example, in most music there is a level of syncopation, which means that the "foot-tapping" beat that we perceive does not correspond to the presence of a physical sound. This means that this is a quite different field to onset detection, which is the detection of the physical sounds, and is performed in a different way.
You could try the Aubio library, which is a plain C library offering both onset and beat extraction tools.
There is also the online Echonest API, although this involves uploading an MP3 to a website and retrieving XML, so might not be so suitable..
EDIT: I came across this last night - a very promising looking C/C++ library, although I haven't used it myself. Vamp Plugins
The general area of research you are interested in is called MUSIC INFORMATION RETRIEVAL
There are many different algorithms that do this but they all are fundamentally centered around ONSET DETECTION.
Onset detection measures the start of an event, the event in this case is a note being played. You can look for changes in the weighted fourier transform (High Frequency Content) you can look for large changes in spectrial content. (Spectrial Difference). (there are a couple of papers that I recommend you look into further down) Once you apply an onset detection algorithm you pick off where the beats are via thresholding.
There are various algorithms that you can use once you've gotten that time localization of the beat. You can turn it into a pulse train (create a signal that is zero for all time and 1 only when your beat happens) then apply a FFT to that and BAM now you have a Frequency of Onsets at the largest peak.
Here are some papers to lead you in the right direction:
https://web.archive.org/web/20120310151026/http://www.elec.qmul.ac.uk/people/juan/Documents/Bello-TSAP-2005.pdf
https://adamhess.github.io/Onset_Detection_Nov302011.pdf
Here is an extension to what some people are discussing:
Someone mentioned looking into applying a machine learning algorithm: Basically collect a bunch of features from the onset detection functions (mentioned above) and combine them with the raw signal in a neural network/logistic regression and learn what makes a beat a beat.
look into Dr Andrew Ng, he has free machine learning lectures from Stanford University online (not the long winded video lectures, there is actually an online distance course)
If you can manage to interface with python code in your project, Echo Nest Remix API is a pretty slick API for python:
There's a method analysis.tempo which will give you the BPM. It can do a whole lot more than simple BPM, as you can see from the API docs or this tutorial
Perform a Fourier transform, and find peaks in the power spectrum. You're looking for peaks below the 20 Hz cutoff for human hearing. I'd guess typically in the 0.1-5ish Hz range to be generous.
SO question that might help: Bpm audio detection Library
Also, here is one of several "peak finding" questions on SO: Peak detection of measured signal
Edit: Not that I do audio processing. It's just a guess based on the fact that you're looking for a frequency domain property of the file...
another edit: It is worth noting that lossy compression formats like mp3, store Fourier domain data rather than time domain data in the first place. With a little cleverness, you can save yourself some heavy computation...but see the thoughtful comment by cobbal.
To repost my answer: The easy way to do it is to have the user tap a button in rhythm with the beat, and count the number of taps divided by the time.
Others have already described some beat-detection methods. I want to add that there are some libraries available that provide techniques and algorithms for this sort of task.
Aubio is one of them, it has a good reputation and it's written in C with a C++ wrapper so you can integrate it easily with a cocoa application (all the audio stuff in Apple's frameworks is also written in C/C++).
There are several methods to get the BPM but the one I find the most effective is the "beat spectrum" (described here).
This algorithm computes a similarity matrix by comparing each short sample of the music with every others. Once the similarity matrix is computed it is possible to get average similarity between every samples pairs {S(T);S(T+1)} for each time interval T: this is the beat spectrum. The first high peak in the beat spectrum is most of the time the beat duration. The best part is you can also do things like music structure or rythm analyses.
I'd imagine this will be easiest in 4-4 dance music, as there should be a single low frequency thud about twice a second.