Created by Zachary A. Pardos (zp@berkeley.edu) and Matthew J. Johnson (mattjj@csail.mit.edu) Computational Approaches to Human Learning Research (CAHL) Lab @ UC Berkeley

This is intended as a quick overview of steps to install and setup and to run xBKT locally.

# Installation and setup

Cloning the repository

git clone git@github.com/CAHLR/xBKT.git

Installing Eigen

Get Eigen from http://eigen.tuxfamily.org/index.php?title=Main_Page and unzip it somewhere (anywhere will work, but it affects the mex command below). On a *nix machine, these commands should put Eigen in /usr/local/include:

cd /usr/local/include
wget --no-check-certificate http://bitbucket.org/eigen/eigen/get/3.1.3.tar.gz
tar -xzvf 3.1.3.tar.gz
ln -s eigen-eigen-2249f9c22fe8/Eigen ./Eigen
rm 3.1.3.tar.gz

Similarly, if working in OS X, you can download the latest stable version of Eigen from the site above. This program has run successfully with Eigen 3.2.5. First move the file to /usr/local/include, then unzip and create simplified link to Eigen. These commands can be used below:

mv <path to file>/3.1.3.tar.gz /usr/local/include/3.1.3.tar.gz
tar -xvf 3.1.3.tar.gz
ln -s <name of unzipped file>/Eigen ./Eigen
rm 3.1.3.tar.gz

Compiling

Run make in the root directory of the xBKT project folder. If this step runs successfully, you should see a MEX file generated for each of the .cpp files.

Potential Errors When Running Makefile on OS X

Before running make, check Makefile in xBKT. Be sure that the MATLABPATH matches your matlab version and EIGENPATH matches your Eigen filepath. For example, if you're working with Matlab 2015 in OS X, you may need to update Makefile with the new name of your Applications from

    ifeq ($(UNAME),Darwin)
        MATLABPATH=/Applications/MATLAB_R2013a.app
    endif

to something like

    ifeq ($(UNAME),Darwin)
        MATLABPATH=/Applications/MATLAB_R2015b.app
    endif

You may see the following error while running make

    make: g++-4.9: No such file or directory

Try gcc --version in your terminal. If a version exists, you already have gcc installed. This error may be due to an incorrect version of gcc being called. In order to change the gcc version in Makefile, update the CXX variable. For example, you may need to change CXX=g++-4.9 to CXX=g++-5, depending on the version you set up.

If a version does not exist, you may need to download gcc49. This can be downloaded with brew.

These steps would allow you to set up gcc49. Run the following commands

    brew install --enable-cxx gcc49
    brew install mpfr
    brew install gmp
    brew install libmpc

# Preparing Data and Running Model # ## Input and Output Data ## `xBKT` models student mastery of a skills as they progress through series of learning resources and checks for understanding. Mastery is modelled as a latent variable has two states - "knowing" and "not knowing". At each checkpoint, students may be given a learning resource (i.e. watch a video) and/or question(s) to check for understanding. The model finds the probability of learning, forgetting, slipping and guessing that maximizes the likelihood of observed student responses to questions.

To run the xBKT model, define the following variables:

• num_subparts: The number of unique questions used to check understanding. Each subpart has a unique set of emission probabilities.
• num_resources: The number of unique learning resources available to students.
• num_fit_initialization: The number of iterations in the EM step.

Next, create an input object Data, containing the following attributes:

• data: a matrix containing sequential checkpoints for all students, with their responses. Each row represents a different subpart, and each column a checkpoint for a student. There are three potential values: {0 = no response or no question asked, 1 = wrong response, 2 = correct response}. If at a checkpoint, a resource was given but no question asked, the associated column would have 0 values in all rows. For example, to set up data containing 5 subparts given to two students over 2-3 checkpoints, the matrix would look as follows:

    | 0  0  0  0  2 |
    | 0  1  0  0  0 |
    | 0  0  0  0  0 |
    | 0  0  0  0  0 |
    | 0  0  2  0  0 |   
  

  In the above example, the first student starts out with just a learning resource, and no checks for understanding. In subsequent checkpoints, this student also responds to subpart 2 and 5, and gets the first wrong and the second correct.

• starts: defines each student's starting column on the data matrix. For the above matrix, starts would be defined as:

    | 1  4 |
  

• lengths: defines the number of check point for each student. For the above matrix, lengths would be defined as:

    | 3  2 |
  

• resources: defines the sequential id of the resources at each checkpoint. Each position in the vector corresponds to the column in the data matrix. For the above matrix, the learning resources at each checkpoint would be structured as:

    | 1  2  1  1  3 |
  

• stateseqs: this attribute is the true knowledge state for above data and should be left undefined before running the xBKT model.

The output of the model can will be stored in a fitmodel object, containing the following probabilities as attributes:

• As: the transition probability between the "knowing" and "not knowing" state. Includes both the learns and forgets probabilities, and their inverse. As creates a separate transition probability for each resource.
• learns: the probability of transitioning to the "knowing" state given "not known".
• forgets: the probability of transitioning to the "not knowing" state given "known".
• prior: the prior probability of "knowing".

The fitmodel also includes the following emission probabilities:

• guesses: the probability of guessing correctly, given "not knowing" state.
• slips: the probability of picking incorrect answer, given "knowing" state.

Running xBKT

You can work in the repository root directory or add it to your path with addpath (no need to use genpath, since everything is organized with namespaces).

To start the EM algorithm, initiate a randomly generated fitmodel, with two potential options:

1. generate.random_model_uni: generates a model from uniform distribution and sets the forgets probability to 0.

2. generate.random_model: generates a model from dirichlet distribution and allows the forgets probability to vary.

For data observed during a short period of learning activity with a low probability of forgetting, the uniform model is recommended. The following example will initiate fitmodel using the uniform distribution:

     fitmodel = generate.random_model_uni(num_resources,num_subparts);

Once the fitmodel is generated, the following function can be used to generate an updated fitmodel and log_likelihoods:

    [fitmodel, log_likelihoods] = fit.EM_fit(fitmodel, data)

If there is an error E_step, you may need to recompile (see Installation and setup).

Example

[TODO: Update Example Model]

See the file +test/hand_specified_model.m for a fairly complete example, which you can run with test.hand_specified_model.

Here's a simplified version:

num_subparts = 4;
truemodel = generate.random_model(num_subparts);

data = generate.synthetic_data(truemodel,[200,150,500]);

best_likelihood = -inf;
for i=1:25
    [fitmodel, log_likelihoods] = fit.EM_fit(generate.random_model(num_subparts),data);
    if (log_likelihoods(end) > best_likelihood)
        best_likelihood = log_likelihoods(end);
        best_model = fitmodel;
    end
end

disp('these two should look similar');
truemodel.A
best_model.A