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Specification for a Functional Reactive Programming language
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I am trying to understand functional reactive programming for a long time (since I have participated in the Reactive Coursera course a year ago) but I still don't understand the essence of it.
Here I am going to describe my current understanding about functional programming vs. functional reactive programming and I would like know if I am on the right path towards understanding the essence of functional reactive programming or not, if not then why not ?
I want to know if it is a good analogy to think about functional reactive programming as programming with differential equations.
In other words, specifying how the system evolves in terms of equations (declaratively).
In functional programming computations are described using static, time-independent equations, in contrast in functional reactive programming everything becomes time dependent. So instead of describing a simple function, one describes a function that depends on time explicitly.
For example, in traditional functional programming one is programming using pure functions without side effects. Just like mathematical functions (maps from one set to another set).
For example f(x)=x^2.
However, in functional reactive programming, to my understanding, and I am not sure if I understand it correctly so please correct me if I am not, one describes computations in terms of time dependent discrete differential equations.
For example, if I want to describe the user interacting with a ball on the screen, which can move along one dimensions (x) then I write the following equations:
x(t)/dt=v(t)
v(t)/dt=a(t)
a(t)=F(t)/m
where F(t) is the force exerted by the user onto the ball.
If I understand correctly, the essence of functional reactive programming is to go from static functions to time dependent functions and express the computations/algorithms in terms of (discrete) differential equations.
Is this understanding of mine correct ? Is this really the essence of functional reactive programming, or is there more to it ?
See my answer here (containing the two essential founding properties of FRP) and follow the links you find.
Related
I'm a computer science student among the things I'm learning Abstract Algebra, especially Group theory.
I'm programming for about 5 years and I've never used such things as I learn in Abstract Algebra.
what is the context between programming and abstract algebra? I really have to know.
Group theory is very important in cryptography, for instance, especially finite groups in asymmetric encryption schemes such as RSA and El Gamal. These use finite groups that are based on multiplication of integers. However, there are also other, less obvious kinds of groups that are applied in cryptography, such as elliptic curves.
Another application of group theory, or, to be more specific, finite fields, is checksums. The widely-used checksum mechanism CRC is based on modular arithmetic in the polynomial ring of the finite field GF(2).
Another more abstract application of group theory is in functional programming. In fact, all of these applications exist in any programming language, but functional programming languages, especially Haskell and Scala(z), embrace it by providing type classes for algebraic structures such as Monoids, Groups, Rings, Fields, Vector Spaces and so on. The advantage of this is, obviously, that functions and algorithms can be specified in a very generic, high level way.
On a meta level, I would also say that an understanding of basic mathematics such as this is essential for any computer scientist (not so much for a computer programmer, but for a computer scientist – definitely), as it shapes your entire way of thinking and is necessary for more advanced mathematics. If you want to do 3D graphics stuff or programme an industry robot, you will need Linear Algebra, and for Linear Algebra, you should know at least some Abstract Algebra.
I don't think there's any context between group theory and programming...or rather your question doesn't make any sense. There are applications of programming to algebra and vice versa but they are not intrinsically tied together or mutually beneficial to one another so to speak.
If you are a computer scientist trying to solve some fun abstract algebras problems, there are numerous enumeration and classification problems that could benefit from a computational approach to be worked on in geometric group theory which is a hot topic at the moment, here's a pretty comprehensive list of researchers and problems (of 3 years ago at least)
http://www.math.ucsb.edu/~jon.mccammond/geogrouptheory/people.html
popular problems include finitely presented groups, classification of transitive permutation groups, mobius functions, polycyclic generating systems
and these
http://en.wikipedia.org/wiki/Schreier–Sims_algorithm
http://en.wikipedia.org/wiki/Todd–Coxeter_algorithm
and a problem that gave me many sleepless nights
http://en.wikipedia.org/wiki/Word_problem_for_groups
Existing algebra systems include GAP and MAGMA
finally an excellent reference
http://books.google.com/books?id=k6joymrqQqMC&printsec=frontcover&dq=finitely+presented+groups+book&hl=en&sa=X&ei=WBWUUqjsHI6-sQTR8YKgAQ&ved=0CC0Q6AEwAA#v=onepage&q=finitely%20presented%20groups%20book&f=false
We know mathematics have both symbolic and numeric computation. But why is Lisp, as a common programming language, connected to symbolic computation more closely?
What parts of Lisp make it good for symbolic problems?
At the time, symbols were a first class object in Lisp, and less so in other languages. Most other languages were focused on numeric computing (1 + 2 + SIN(PI / 2)).
In Lisp, the Symbol is a specific language artifact (distinct from a character string) that made working with Things That Aren't Numbers very easy. Since these were first class objects within the system, Lisp provided "free" parsers, readers, and writers of such objects.
'(A + B / 2) was trivial to represent in off the shelf Lisp.
The ease of representation lifted the burden of reading and writing those aspects of a symbolic computing application, making it easier to focus on the core problems (equation reduction, problem solver, theorem proofs, etc.)
Today, even still, few languages have a first class concept of the Symbol. But there are enough utilities and such that they are less important today than they were back in the day when it was basic Lisp vs Fortan vs Pascal for this kind of work.
The term symbolic computation often associated with Lisp is baffling to millennials who grew up in an age where computers are used in all areas of human and social life. Back in the day when Lisp appeared, computers were expensive and their use was primarily used in a scientific/accounting context. Number crunching. Translating known algorithms from Mathematics into programs. One area where existing languages had trouble solving problems elegantly was algebraic formulas with polynomial expressions. Lisp provided first-class constructs that enabled the design of computer algebra systems that mapped seamlessly with traditional mathematical reasoning, hence the term. Symbolic computation is still relevant today, particularly in the fields of logic programming, constraint solving, artificial intelligence, etc.
In LISP you can enter a symbol without predeclaration. Also, complex data structures are supported as linked lists of arbitrary complexity. Since manipulation of symbols is best accomplished in the context of complex data structures, LISP is a perfect fit. Additionally, when using complex data structures to model a problem other languages require you to spend a lot of effort in walking the data structures. In lisp the data structure traversal is automated and you can work at a higher level of abstraction.
Do you know if anyone has tried to compile high level programming languages (java, c#, etc') into a recurrent neural network and then evolve them?
I mean that the whole process including memory usage is stored in a graph of a neural net, and I'm talking about complex programs (thinking about natural language processing problems).
When I say neural net I mean a directed weighted graphs that spreads activation, and the nodes are functions of their inputs (linear, sigmoid and multiplicative to keep it simple).
Furthermore, is that what people mean in genetic programming or is there a difference?
Neural networks are not particularly well suited for evolving programs; their strength tends to be in classification. If anyone has tried, I haven't heard about it (which considering I barely touch neural networks is not a surprise, but I am active in the general AI field at the moment).
The main reason why neural networks aren't useful for generating programs is that they basically represent a mathematical equation (numeric, rather than functional). Given some numeric input, you get a numeric output. It is difficult to interpret these in the context of a program any more complicated than simple arithmetic.
Genetic Programming traditionally uses Lisp, which is a pure functional language, and often programs are often shown as tree diagrams (which occasionally look similar to some neural network diagrams - is this the source of your confusion?). The programs are evolved by exchanging entire branches of a tree (a function and all its parameters) between programs or regenerating an entire branch randomly.
There are certainly a lot of good (and a lot of bad) references on both of these topics out there - I refrain from listing them because it isn't clear what you are actually interested in. Wikipedia covers each of these techniques, and is a good starting point.
Genetic programming is very different from Neural networks. What you are suggesting is more along the lines of genetic programming - making small random changes to a program, possibly "breeding" successful programs. It is not easy, and I have my doubts that it can be done successfully across a large program.
You may have more luck extracting a small but critical part of your program, one which has a few particular "aspects" (such as parameter values) that you can try to evolve.
Google is your friend.
Some sophisticated anti-virus programs as well as sophisticated malware use formal grammar and genetic operators to evolve against each other using neural networks.
Here is an example paper on the topic: http://nexginrc.org/nexginrcAdmin/PublicationsFiles/raid09-sadia.pdf
Sources: A class on Artificial Intelligence I took a couple years ago.
With regards to your main question, no one has ever tried that on programming languages to the best of my knowledge, but there is some research in the field of evolutionary computation that could be compared to something like that (but it's obviously a far-fetched comparison). As a matter of possible interest, I asked a similar question about sel-improving compilers a while ago.
For a difference between genetic algorithms and genetic programming, have a look at this question.
Neural networks have nothing to do with genetic algorithms or genetic programming, but you can obviously use either to evolve neural nets (as any other thing for that matters).
You could have look at genetic-programming.org where they claim that they have found some near human competitive results produced by genetic programming.
I have not heard of self-evolving and self-imrpvoing programs before. They may exist as special research tools like genetic-programming.org have but nothing solid for generic use. And even if they exist they are very limited to special purpose operations like malware detection as Alain mentioned.
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A professor asked me to help making a specification for a college project.
By the time the students should know the basics of programming.
The professor is a mathematician and has little experience in other programming languages, so it should really be in MATLAB.
I would like some projects ideas. The project should
last about 1 to 2 months
be done individually
have web interface would be great
doesn't necessary have to go deep in maths, but some would be great
use a database (or store data in files)
What kind of project would make the students excited?
If you have any other tips I'll appreciate.
UPDATE: The students are sophomores and have already studied vector calculus. This project is for an one year Discrete Mathematics course.
UPDATE 2: The topics covered in the course are
Formal Logic
Proofs, Recursion, and Analysis of Algorithms
Sets and Combinatorics
Relations, Functions, and Matrices
Graphs and Trees
Graph Algorithms
Boolean Algebra and Computer Logic
Modeling Arithmetic, Computation, and Languages
And it'll be based on this book Mathematical Structures for Computer Science: A Modern Approach to Discrete Mathematics by Judith L. Gersting
General Suggestions:
There are many teaching resources at The MathWorks that may give you some ideas for course projects. Some sample links:
The MATLAB Central blogs, specifically some posts by Loren that include using LEGO Mindstorms in teaching and a webinar about MATLAB for teaching (note: you will have to sign up to see the webinar)
The Curriculum Exchange: a repository of course materials
Teaching with MATLAB and Simulink: a number of other links you may find useful
Specific Suggestions:
One of my grad school projects in non-linear dynamics that I found interesting dealt with Lorenz oscillators. A Lorenz oscillator is a non-linear system of three variables that can exhibit chaotic behavior. Such a system would provide an opportunity to introduce the students to numerical computation (iterative methods for simulating systems of differential equations, stability and convergence, etc.).
The most interesting thing about this project was that we were using Lorenz oscillators to encode and decode signals. This "encrypted communication" aspect was really cool, and was based on the following journal article:
Kevin M. Cuomo and Alan V. Oppenheim,
Circuit Implementation of Synchronized Chaos with Applications
to Communications, Physical Review
Letters 71(1), 65-68 (1993)
The article addresses hardware implementations of a chaotic communication system, but the equivalent software implementation should be simple enough to derive (and much easier for the students to implement!).
Some other useful aspects of such a project:
The behavior of the system can be visualized in 2-D and 3-D plots, thus exposing the students to a number of graphing utilities in MATLAB (PLOT, PLOT3, COMET, COMET3, etc.).
Audio signals can be read from files, encrypted using the Lorenz equations, written out to a new file, and then decrypted once again. You could even have the students each encrypt a signal with their Lorenz oscillator code and give it to another student to decrypt. This would introduce them to various file operations (FREAD, FWRITE, SAVE, LOAD, etc.), and you could even introduce them to working with audio data file formats.
You can introduce the students to the use of the PUBLISH command in MATLAB, which allows you to format M-files and publish them to various output types (like HTML or Word documents). This will teach them techniques for making useful help documentation for their MATLAB code.
I have found that implementing and visualizing Dynamical systems is great
for giving an introduction to programming and to an interesting branch of
applied mathematics. Because one can see the 'life' in these systems,
our students really enjoy this practical module.
We usually start off by visualizing a 1D attractor, so that we can
overlay the evolution rule/rate of change with the current state of
the system. That way you can teach computational aspects (integrating the system) and
visualization, and the separation of both in implementation (on a simple level, refreshing
graphics at every n-th computation step, but in C++ leading to threads, unsure about MATLAB capabilities here).
Next we add noise, and then add a sigmoidal nonlinearity to the linear attractor. We combine this extension with an introduction to version control (we use a sandbox SVN repository for this): The
students first have to create branches, modify the evolution rule and then merge
it back into HEAD.
When going 2D you can simply start with a rotation and modify it to become a Hopf oscillator, and visualize either by morphing a grid over time or by going 3D when starting with a distinct point. You can also visualize the bifurcation diagram in 3D. So you again combine generic MATLAB skills like 3D plotting with the maths.
To link in other topics, browse around in wikipedia: you can bring in hunter/predator models, chaotic systems, physical systems, etc.etc.
We usually do not teach object-oriented-programming from within MATLAB, although it is possible and you can easily make up your own use cases in the dynamical systems setting.
When introducing inheritance, we will already have moved on to C++, and I'm again unaware of MATLAB's capabilities here.
Coming back to your five points:
Duration is easily adjusted, because the simple 1D attractor can be
done quickly and from then on, extensions are ample and modular.
We assign this as an individual task, but allow and encourage discussion among students.
About the web interface I'm at a loss: what exactly do you have in mind, why is it
important, what would it add to the assignment, how does it relate to learning MATLAB.
I would recommend dropping this.
Complexity: A simple attractor is easily understood, but the sky's the limit :)
Using a database really is a lot different from config files. As to the first, there
is a database toolbox for accessing databases from MATLAB. Few institutes have the license though, and apart from that: this IMHO does not belong into such a course. I suggest introducing to the concept of config files, e.g. for the location and strength of the attractor, and later for the system's respective properties.
All this said, I would at least also tell your professor (and your students!) that Python is rising up against MATLAB. We are in the progress of going Python with our tutorials, but I understand if someone wants to stick with what's familiar.
Also, we actually need the scientific content later on, so the usefulness for you will probably depend on which department your course will be related to.
A lot of things are possible.
The first example that comes in mind is to model a public transportation network (the network of your city, with underground, buses, tramways, ...). It is represented by a weighted directed graph (you can use sparse matrix to represent it, for example).
You may, for example, ask them to compute the shortest path from one station to another one (Moore-dijkistra algorithm, for example) and display it.
So, for the students, the several steps to do are:
choose an appropriate representation for the network (it could be some objects to represent the properties of the stations and the lines, and a sparse matrix for the network)
load all the data (you can provide them the data in an XML file)
be able to draw the network (since you will put the coordinates of the stations)
calculate the shortest path from one point to another and display it in a pretty way
create a fronted (with GUI)
Of course, this could be complicated by adding connection times (when you change from one line to another), asking for several options (shortest path with minimum connections, take in considerations the time you loose by waiting for a train/bus, ...)
The level of details will depend on the level of the students and the time they could spend on it (it could be very simple, or very realist)
You want to do a project with a web interface and a database, but not any serious math... and you're doing it in MATLAB? Do you understand that MATLAB is especially designed to be used for "deep math", and not for web interfaces or databases?
I think if this is an intro to a Discrete Mathematics course, you should probably do something involving Discrete Mathematics, and not waste the students' time as they learn a bunch of things in that language that they'll never actually use.
Why not do something involving audio? I did an undergraduate project in which we used MATLAB to automatically beat-match different tunes and DJ mix between them. The full program took all semester, but you could do a subset of it. wavread() and the like are built in and easy to use.
Or do some simple image processing like finding Waldo using cross-correlation.
Maybe do something involving cryptography, have them crack a simple encryption scheme and feel like hackers.
MATLAB started life as a MATrix LAB, so maybe concentrating on problems in linear algebra would be a natural fit.
Discrete math problems using matricies include:
Spanning trees and shortest paths
The marriage problem (bipartite graphs)
Matching algorithms
Maximal flow in a network
The transportation problem
See Gil Strang's "Intro to Applied Math" or Knuth's "Concrete Math" for ideas.
You might look here: http://www.mathworks.com/academia/student_center/tutorials/launchpad.html
on the MathWorks website. The interactive tutorial (second link) is quite popular.
--Loren
I always thought the one I was assigned in grad school was a good choice-a magnetic lens simulator. The math isn't completely overwhelming so you can focus more on learning the language, and it's a good intro to the graphical capabilities (e.g., animating the path of an off-axis electron going through the lens).
db I/O and fancy interfaces are out of place in a discrete math course.
my matlab labs were typically algorithm implementations, with charts as output, and simple file input.
how hard is the material? image processing is really easy in matlab, can you do some discrete 2D filtering? blurs and stuff. http://homepages.inf.ed.ac.uk/rbf/HIPR2/filtops.htm
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Closed 14 years ago.
Duplicate of How to program a fractal
What are fractals?
Is this is one of the concepts that is brought over from Mathematics to programming to simplify or solve a particular set of problems?
I am closing this question and have posted a related question
If you want to know about fractals in a general non-programming way, I would suggest looking at a general non-programming site. Wikipedia has a good article on them. If you want to know about programming fractals, I would suggest looking at this already asked question:
How to program a fractal
It even has a fractal tag.
A fractal is generally "a rough or fragmented geometric shape that can be split into parts, each of which is (at least approximately) a reduced-size copy of the whole," a property called self-similarity. The term was coined by Benoît Mandelbrot in 1975 and was derived from the Latin fractus meaning "broken" or "fractured." A mathematical fractal is based on an equation that undergoes iteration, a form of feedback based on recursion.
A fractal often has the following features:
It has a fine structure at arbitrarily small scales.
It is too irregular to be easily described in traditional Euclidean geometric language.
It is self-similar (at least approximately or stochastically).
It has a Hausdorff dimension which is greater than its topological dimension (although this requirement is not met by space-filling curves such as the Hilbert curve).
It has a simple and recursive definition.
http://en.wikipedia.org/wiki/Fractal
its a type of self-similar shape, often grounded in a repeated mathematical function (but not necessarily). It has nothing to do with programming technique, but the easiest way to view one is to write a program to draw it. (drawing a fractal with pen-and-paper is pretty time-consuming)
By 'self-similar' i mean, if you keep zooming in on different parts of the fractal, it doesn't get any "smoother" or more linear, as would happen with a non-fractal shape. It's degree of complexity is invariant of the zoom level.
the Wikipedia page is pretty useful
Look up Procedural Generation for one way of how fractals are used in programming. They are an excellent way of generating chaotic/seemingly complex data from a very simple source. The generated data often benefits from self-similarity and other bits of organzation that make the content make more sense to people.