# Getting Started¶

The cdr package provides utilities that support easy training and evaluation of CDR models. Most of these utilities depend on a config file *.ini containing metadata needed to construct the CDR model(s). At training time, a copy of the config file is placed in the output directory for the experiment, which can be useful for record keeping. The approach of using config files rather than command line arguments to define experiments has several advantages:

• Users only need to define the experiment once, and settings can be reused for arbitrarily many models

• The config file contains a permanent record of the settings used in the experiment, facilitating later reproduction

• The config file can be shared across many utilities (training, evaluation, statistical testing, plotting, etc.)

This guide describes how to write the config file and use it to train and evaluate CDR(NN) models.

## Configuring CDR(NN) Experiments¶

A set of CDR experiments is definied in a config file *.ini, which can then be passed to CDR executables. For example, once a config file foo.ini has been created, the models defined in it can be trained using the included train executable, like so::

python -m cdr.bin.train foo.ini


The config file must at minimum contain the sections [data] (with pointers to training/evaluation data) and [global_settings] (with the location of the output directory). A section [cdr_settings] can be (optionally) provided to override default settings. In addition, the config file should contain at least one model section, consisting of the prefix model_CDR_ (for CDR) or model_CDRNN_ (for CDRNN) followed by a custom name for the model. For example, to define a CDR model called readingtimes, use the section heading [model_CDR_readingtimes]. The identifier CDR_readingtimes will then be used by a number of utilities to designate this model (the reason CDR must be included in the prefix is that this repository distributes with unofficial support for running LM, LME, and GAM models from the same interface). The data and settings configurations will be shared between all models defined a single config file. Each model section heading should contain at least the field formula. The value provided to formula must be a valid CDR model string. Additional fields may be provided to override inherited CDR settings on a model-specific basis. Experiments involving distinct datasets require distinct config files.

For more details on the available configuration parameters, see CDR Configuration Files. For more details on CDR model formulae, see CDR Model Formulas. To jump-start a new config file, run:

python -m cdr.bin.create_config > PATH.ini


Add the flag -t cdrnn to generate a CDRNN-oriented config, and add the flag -a to include annotations that can help you fill in the fields correctly.

## Running CDR executables¶

A number of executable utilities are contained in the module cdr.bin and can be executed using Python’s -m flag. For example, the following call runs the train utility on all models specified in a config file config.ini::

python -m cdr.bin.train config.ini


Usage help for each utility can be viewed by running::

python -m cdr.bin.<UTIL-NAME> -h


for the utility in question. Or usage help for all utilities can be printed at once using::

python -m cdr.bin.help


The following sections go into more detail about training and evaluation utilities that will likely be useful to most users.

## Training CDR(NN) Models¶

First, gather some data and write a config file defining your experiments. Note that CDR utilities assume the data will be saved in a space-delimited text file, a requirement that facilitates interoperability with the [Modelblocks repository](https://github.com/modelblocks/modelblocks-release), which can be used to generate and preprocess data for many psycholinguistic experiments. Once the config file has been written, training a CDR model is simple using the train utility, which takes as its principle argument a path to the config file. For example, if the config file is names experiment.ini, all models defined in it can be trained with the call::

python -m dstr.bin.train experiment.ini


To restrict training to some subset of models, the -m flag is used. For example, the following call trains models A and B only::

python -m cdr.bin.train experiment.ini -m CDR_A CDR_B


CDR periodically saves training checkpoints to the model’s output directory (every save_freq training epochs, where save_freq can be defined in the config file or left at its default of 1). This allows training to be interrupted and resumed. To save space, checkpoints overwrite each other, so the output directory will contain only the most recent checkpoint. If the train utility discovers a checkpoint in the model’s output directory, it loads it and resumes training from the saved state. This feature can also be used to add training epochs after termination in the event of model non-convergence. Simply increase the number of training iterations specified in the config file and rerun train, and the model will continue training until it hits the new maximum number of epochs.

CDR uses the history of losses by training iteration to automatically diagnose convergence and stop training, but it’s still a good idea to visually inspect learning curves to make sure nothing horrible has happened during the training process (e.g. large loss spikes, which signal a problem and can confuse the convergence checker). CDR learning curves can be visualized in Tensorboard. To run Tensorboard for a CDR model called CDR_A saved in experiment directory EXP, run:

python -m tensorboard.main --logdir=EXP/CDR_A


then open the returned address (usually http://<USERNAME>:6006) in a web browser.

## Evaluating CDR(NN) Models¶

This package provides several utilities for inspecting and evaluating fitted CDR models. The principal evaluation utility is predict. The following generates predictions on test data from the model CDR_A defined in experiment.ini::

python -m cdr.bin.predict experiment.ini -m CDR_A -p test


This call will save files containing elementwise predictions, errors, and likelihoods, along with a performance summary. For more details on usage, run::

python -m cdr.bin.predict -h


Once predict has been run for multiple models, statistical model comparison (permutation test) can be performed using compare, as shown::

python -m cdr.bin.compare experiment.ini -p test


The above call will permutation test pairwise differences in mean squared error on test data for all unique pairs of models defined in experiment.ini.

In addition to these core utilities, convolve convolves the input predictors using the fitted CDR data transform and saves the data table, and make_plots generates IRF plots with basic customization as permitted by the command line arguments.

## CDR(NN) Model Comparison¶

Two or more CDR(NN) models can be statistically compared using bootstrap testing (specifically, paired permutation tests). This repository provides utilities to support this. To compare models CDR_A and CDR_B using a mean squared error test statistic on the test partition designated in the *.ini file, run:

python -m cdr.bin.pt experiment.ini -m CDR_A CDR_B -M err -p test


Models can also be compared using a likelihood difference test statistic:

python -m cdr.bin.pt experiment.ini -m CDR_A CDR_B -M loglik -p test


If you specified ablations within the model definition using the ablate keyword (see CDR Configuration Files), you can test all single-variable nested ablations in a config file as follows:

python -m cdr.bin.pt experiment.ini -a -M loglik -p test


A separate utility (ct) is also provided to permutation test the difference in correlation between true and predicted responses:

python -m cdr.bin.ct experiment.ini -a -p test


The properties of each of these test statistics govern which is most appropriate to use. Error-based tests are useful for comparing qualitatively different models whose likelihood functions are either not available or not directly comparable (e.g. CDR vs. LME). Likelihood-based tests are useful for comparing CDR models with non-normal error (e.g sinh-arcsinh). Correlation-based tests are useful when the primary emphasis is on the strength of linear relationship between predictions and response, abstracting away from shift and scale.

Full usage for these bootstrapping utilities can be viewed by running:

python -m cdr.bin.help pt ct