For example,
I want to create an AI that plays Ticktacktoe, this is how I would go about it.
I have 9 input nodes which is for each space on the board, 3 nodes for one hidden layer (which I'm guessing would somehow benefit the AI by having it select a row or column with 3 spaces), and then 9 output nodes to see where the AI would put its mark on the entire board.
I'm lost on how I would find the cost of this neural network because I don't know how I would judge its prediction and affect its weights and biases.
If I wanted the AI to play a guessing game, it would make sense since I have the correct answer and I can teach it to be more accurate based on how off it was to the actual answer.
(NOTE: I am very new to neural networks, so there may be a simple answer that I've missed somewhere)
So, I did some digging around and found a good introduction to reinforcement learning. This is the method that is used to train neural networks to achieve a goal without knowing an exact target like which move is good in a certain scenario. Backpropagation is not the only learning method, but so many sources only used this method without letting the viewer know of any other methods which confused me.
Going through this playlist right now: https://www.youtube.com/watch?v=2pWv7GOvuf0&index=1&list=PL7-jPKtc4r78-wCZcQn5IqyuWhBZ8fOxT
Hope this will help someone getting started with neural networks!
Related
What i mean is games like chess, draughts, tic tac toe, 2048, Super Mario?, in general games that require multiple plays, moves to complete.
I'm pretty sure one could use Genetic Algorithms, but i'm willing to know if there's a way to train it with pure backpropagation. What would I use as target values?
I was thinking of letting him play a number of moves until the game ends and use the end result as target values, but i think that would only train the last move, won't it?
The other approach would be to train every move, but then what would the target values be? You can have multiple valid choices move-by-move, but surely enough one is better on the long-term. How to choose it without me trial-and-error'ing it out?
Is it just not possible to achieve with Backprop?
It is definitely possible, but you have to provide very well determined training data. You have to generate ALL possible board positions, and then programmatically figure out which move is best for that position. You could basically generate all movements using minimax for example.
The best way of doing what you want is to collect input:output data of human players that tend to play a game very well, you then backpropagate these values with dropout enabled to make sure that the network notices the big patterns.
I have an old project of mine which teaches a neural network to learn based on your playing style (neuraldino), although I was quite a newbie then with neural networks so it might not be that effective.
I recently started learning neural networks, and I thought that creating a sudoku solver would be a nice application for NN. I started learning them with backward propagation neural network, but later I figured that there are tens of neural networks. At this point, I find it hard to learn all of them and then pick an appropriate one for my purpose. Hence, I am asking what would be a good choice for creating this solver. Can back propagation NN work here? If not, can you explain why and tell me which one can work.
Thanks!
Neural networks don't really seem to be the best way to solve sudoku, as others have already pointed out. I think a better (but also not really good/efficient) way would be to use an genetic algorithm. Genetic algorithms don't directly relate to NNs but its very useful to know how they work.
Better (with better i mean more likely to be sussessful and probably better for you to learn something new) ideas would include:
If you use a library:
Play around with the networks, try to train them to different datasets, maybe random numbers and see what you get and how you have to tune the parameters to get better results.
Try to write an image generator. I wrote a few of them and they are stil my favourite projects, with one of them i used backprop to teach a NN what x/y coordinate of the image has which color, and the other aproach combines random generated images with ine another (GAN/NEAT).
Try to use create a movie (series of images) of the network learning to create a picture. It will show you very well how backprop works and what parameter tuning does to the results and how it changes how the network gets to the result.
If you are not using a library:
Try to solve easy problems, one after the other. Use backprop or a genetic algorithm for training (whatever you have implemented).
Try to improove your implementation and change some things that nobody else cares about and see how it changes the results.
List of 'tasks' for your Network:
XOR (basically the hello world of NN)
Pole balancing problem
Simple games like pong
More complex games like flappy bird, agar.io etc.
Choose more problems that you find interesting, maybe you are into image recognition, maybe text, audio, who knows. Think of something you can/would like to be able to do and find a way to make you computer do it for you.
It's not advisable to only use your own NN implemetation, since it will probably not work properly the first few times and you'll get frustratet. Experiment with librarys and your own implementation.
Good way to find almost endless resources:
Use google search and add 'filetype:pdf' in the end in order to only show pdf files. Search for neural network, genetic algorithm, evolutional neural network.
Neither neural nets not GAs are close to ideal solutions for Sudoku. I would advise to look into Constraint Programming (eg. the Choco or Gecode solver). See https://gist.github.com/marioosh/9188179 for example. Should solve any 9x9 sudoku in a matter of milliseconds (the daily Sudokus of "Le monde" journal are created using this type of technology BTW).
There is also a famous "Dancing links" algorithm for this problem by Knuth that works very well https://en.wikipedia.org/wiki/Dancing_Links
Just like was mentioned in the comments, you probably want to take a look at convolutional networks. You basically input the sudoku bord as an two dimensional 'image'. I think using a receptive field of 3x3 would be quite interesting, and I don't really think you need more than one filter.
The harder thing is normalization: the numbers 1-9 don't have an underlying relation in sudoku, you could easily replace them by A-I for example. So they are categories, not numbers. However, one-hot encoding every output would mean a lot of inputs, so i'd stick to numerical normalization (1=0.1, 2 = 0.2, etc.)
The output of your network should be a softmax with of some kind: if you don't use softmax, and instead outupt just an x and y coordinate, then you can't assure that the outputedd square has not been filled in yet.
A numerical value should be passed along with the output, to show what number the network wants to fill in.
As PLEXATIC mentionned, neural-nets aren't really well suited for these kind of task. Genetic algorithm sounds good indeed.
However, if you still want to stick with neural-nets you could have a look at https://github.com/Kyubyong/sudoku. As answered Thomas W, 3x3 looks nice.
If you don't want to deal with CNN, you could find some answers here as well. https://www.kaggle.com/dithyrambe/neural-nets-as-sudoku-solvers
I'm implementing Othello using Artificial neural network. When I read document (here, page 19), I don't understand some points.
They calculate the output:
image
I dont know if they calculate that, how this my AI know what the legal moves in game to choose the best legal move. That ouput is only a float number (I think so) and how I can use it?
The good news
It's super simple: the Neural-Network (NN) is a Value-Network (instead of a Policy-Network). This Value-Network takes a board-state as input and calculates some score describing how good the position is. It's the basic building-block of all Minimax-based Game-AIs, often called the evaluation function. (A Policy-Network output would give a probability-distribution over all possible moves)
So the NN gives you this score. You can then combine this score with some algorithm of your choice. Minimax (nearly all Chess-AIs) and MCTS (AlphaGo) are the most common.
Basic idea of Minimax: play a move, opponent plays a move, (repeat), evaluate with your NN -> do this for all possible combinations and propagate with Minimax. Only a few ply's (half-moves) will be possible with this NN, but it will be very powerful for Othello and it's easy to implement.
Basic idea of MCTS: play random move, play random move, (repeat), until game ends -> build-winner statistic. Now compare the average scores of all possible "first" moves. Pick the best. (Harder to incorporate NN as a heuristic.)
The calculation you mentioned is just the classic rule in Neural Networks to define the activation together with a dense-layer.
The bad news
I didn't read the paper, but the hard thing is to train and prepare your NN. You need to provide some data. Maybe it will be supervised (if you have historical games; easier), maybe unsupervised (Q-learning and co.). This will be very hard to do without experience.
I think I know all the theory needed, but I still failed to do this with some other (stochastic) games, because there are many many issues with autocorrelation and co, there is also a lot of hyperparameter-tuning needed.
Conclusion
This project is kind of complicated and there are many many pitfalls. Please be sure you understand the algorithms you want to try. It looks like you are kind of missing the basics. Game-theory (Minimax), AI/Learning-Theory (MCTS, Markov-Decision-Processes, Q-Learning...), NN (basic internals of a NN).
I am trying to make a neural network for approximation of some unkown function (for my neural network course). The problem is that this function has very many variables but many of them are not important (for example in [f(x,y,z) = x+y] z is not important). How could I design (and learn) network for this kind of problem?
To be more specific the function is an evaluation function for some board game with unkown rules and I need to somehow learn this rules by experience of the agent. After each move the score is given to the agent so actually it needs to find how to get max score.
I tried to pass the neighborhood of the agent to the network but there are too many variables which are not important for the score and agent is finding very local solutions.
If you have a sufficient amount of data, your ANN should be able to ignore the noisy inputs. You also may want to try other learning approaches like scaled conjugate gradient or simple heuristics like momentum or early stopping so your ANN isn't over learning the training data.
If you think there may be multiple, local solutions, and you think you can get enough training data, then you could try a "mixture of experts" approach. If you go with a mixture of experts, you should use ANNs that are too "small" to solve the entire problem to force it to use multiple experts.
So, you are given a set of states and actions and your target values are the score after the action is applied to the state? If this problem gets any hairier, it will sound like a reinforcement learning problem.
Does this game have discrete actions? Does it have a discrete state space? If so, maybe a decision tree would be worth trying?
How do you train Neural Network for pattern recognition? For example a face recognition in a picture how would you define the output neurons? (eg. how to detect where is the face exactly, rather than just saying that there is a face in camera). Also, how about detecting multiple faces and different size of faces?
If anyone could give me a pointer it would be really great
Cheers!
Generally speaking I would split the problem into multiple stages e.g.
1 - Is there a face in the picture?
2 - Where is the face in the picture?
3 - Is the face in the picture one that the NN (Neural network) recognises?
In each instance I would suggest you build a separate NN and train it to answer the questions posed.
As for the structure of the NN, that's a bit trickier to answer as it depends on your input data and desired output. For example if you had a 100x100 px image then I suppose its feasible to have 10,000 inputs. You might want to consider doing some preprocessing before hand to say detect ovals that way you could look and see if there are a number of ovals in a predictable outline (1 for the face, 2 for the eyes, and one for the mouth possibly). If you are preprocessing the data then you might have inputs for each oval.
Now for the output... for question one you could just have one output to say how sure the NN is that there is a face in the input data i.e a valuer of 0.0 (defiantly no face) --> 1.0 (defiantly a face). This way you can move onto stages 2 and 3.
I might say at this point that this is a non-trivial problem and you might be better to have a look at some of the frameworks available e.g. OpenCV
Now for the training part, you need to have a stockpile of images available to train the NN. There are a number of ways in which you could train the NN. One potential solution is to use a technique called back propagation 1, 2. In general terms, you use the NN on an image and compare it to a predetermined output. If its wrong tweak the NN to produce the desired output and repeat.
If you want a good book on AI, then I would highly recommend Artificial Intelligence: A Modern Approach by Russell and Norvig. Im sure that there are more appropriate Computer Vision textbooks, but the Russell & Norvig book is an excellent starter.
Dear GantengX, you should prepare your self to the fact that the answer is so large, complex and hard to understand. There is so many approaches to pattern and face recognition. And implementing real-life face recognition system is a huge array of work that one person can never handle. Prepare your self for at least 10 years of life behind books on mathematic and artificial intelligence, I'm not talking about hiring 5 highly payed developers in the end who will understand what you want them to do. And maybe you will end up having your own face recognition system. There are also dozen of other issues that will jump out during the process. So be ready for a life full of stresses and problems.
I'm sorry for telling obvious things, but your question was not specific, complete answer would touch many different scientific spheres and will result as a book with over 1k pages.
Regarding your question (the short answer).
There are several principal parts that each face recognition app consists of:
Artificial intelligence algorithm
Optimization algorithm (for AI optimization)
Different filtration algorithms
Effective data set development
Items 1. and 2. are the central part of each system, they do the actual work. Any other preprocessing just makes the input data less complex, making it easier to do a decision for your AI. Don't start 3. and 4. until you will have your first results.
P.S.
Using existing solutions is more cost-effective, but if you are studying things then don't loose time like I did, and start your dissertation right away.