mlpack_lmnn(1)

NAME
mlpack_lmnn - large margin nearest neighbors (lmnn)

SYNOPSIS
 mlpack_lmnn -i unknown [-b int] [-C bool] [-d unknown] [-k int] [-l unknown] [-L bool] [-n int] [-N bool] [-O string] [-p int] [-P bool] [-A int] [-r double] [-s int] [-a double] [-t double] [-R int] [-V bool] [-c unknown] [-o unknown] [-D unknown] [-h -v]

DESCRIPTION

This program implements Large Margin Nearest Neighbors, a distance learning technique. The method seeks to improve k-nearest-neighbor classification on a dataset. The method employes the strategy of reducing distance between similar labeled data points (a.k.a target neighbors) and increasing distance between differently labeled points (a.k.a impostors) using standard optimization techniques over the gradient of the distance between data points.

To work, this algorithm needs labeled data. It can be given as the last row of the input dataset (specified with '--input_file (-i)'), or alternatively as a separate matrix (specified with '--labels_file (-l)'). Additionally, a starting point for optimization (specified with '--distance_file (-d)'can be given, having (r x d) dimensionality. Here r should satisfy 1 <= r <= d, Consequently a Low-Rank matrix will be optimized. Alternatively, Low-Rank distance can be learned by specifying the '--rank (-A)'parameter (A Low-Rank matrix with uniformly distributed values will be used as initial learning point).

The program also requires number of targets neighbors to work with ( specified with '--k (-k)'), A regularization parameter can also be passed, It acts as a trade of between the pulling and pushing terms (specified with ’--regularization (-r)'), In addition, this implementation of LMNN includes a parameter to decide the interval after which impostors must be re-calculated (specified with '--update_interval (-R)').

Output can either be the learned distance matrix (specified with ’--output_file (-o)'), or the transformed dataset (specified with ’--transformed_data_file (-D)'), or both. Additionally mean-centered dataset (specified with '--centered_data_file (-c)') can be accessed given mean-centering (specified with '--center (-C)') is performed on the dataset. Accuracy on initial dataset and final transformed dataset can be printed by specifying the '--print_accuracy (-P)'parameter.

This implementation of LMNN uses AdaGrad, BigBatch_SGD, stochastic gradient descent, mini-batch stochastic gradient descent, or the L_BFGS optimizer.

AdaGrad, specified by the value 'adagrad' for the parameter '--optimizer (-O)', uses maximum of past squared gradients. It primarily on six parameters: the step size (specified with '--step_size (-a)'), the batch size (specified with '--batch_size (-b)'), the maximum number of passes (specified with ’--passes (-p)'). Inaddition, a normalized starting point can be used by specifying the '--normalize (-N)' parameter.

BigBatch_SGD, specified by the value 'bbsgd' for the parameter '--optimizer (-O)', depends primarily on four parameters: the step size (specified with ’--step_size (-a)'), the batch size (specified with '--batch_size (-b)'), the maximum number of passes (specified with '--passes (-p)'). In addition, a normalized starting point can be used by specifying the '--normalize (-N)' parameter.

Stochastic gradient descent, specified by the value 'sgd' for the parameter ’--optimizer (-O)', depends primarily on three parameters: the step size (specified with '--step_size (-a)'), the batch size (specified with ’--batch_size (-b)'), and the maximum number of passes (specified with ’--passes (-p)'). In addition, a normalized starting point can be used by specifying the '--normalize (-N)' parameter. Furthermore, mean-centering can be performed on the dataset by specifying the '--center (-C)'parameter.

The L-BFGS optimizer, specified by the value 'lbfgs' for the parameter ’--optimizer (-O)', uses a back-tracking line search algorithm to minimize a function. The following parameters are used by L-BFGS: '--max_iterations (-n)', '--tolerance (-t)'(the optimization is terminated when the gradient norm is below this value). For more details on the L-BFGS optimizer, consult either the mlpack L-BFGS documentation (in lbfgs.hpp) or the vast set of published literature on L-BFGS. In addition, a normalized starting point can be used by specifying the '--normalize (-N)' parameter.

By default, the AMSGrad optimizer is used.

Example - Let's say we want to learn distance on iris dataset with number of targets as 3 using BigBatch_SGD optimizer. A simple call for the same will look like:

$ mlpack_lmnn --input_file iris.csv --labels_file iris_labels.csv --k 3 --optimizer bbsgd --output_file output.csv

Another program call making use of update interval & regularization parameter with dataset having labels as last column can be made as:

$ mlpack_lmnn --input_file letter_recognition.csv --k 5 --update_interval 10 --regularization 0.4 --output_file output.csv

REQUIRED INPUT OPTIONS

--input_file (-i) [unknown]
    Input dataset to run LMNN on.

OPTIONAL INPUT OPTIONS

--batch_size (-b) [int]
    Batch size for mini-batch SGD. Default value 50.

--center (-C) [bool]
    Perform mean-centering on the dataset. It is useful when the centroid of the data is far from the origin.

--distance_file (-d) [unknown]
    Initial distance matrix to be used as starting point

--help (-h) [bool]
    Default help info.

--info [string]
    Print help on a specific option. Default value ''.

--k (-k) [int]
    Number of target neighbors to use for each datapoint. Default value 1. --labels_file (-l) [unknown] Labels for input dataset.

--linear_scan (-L) [bool]
    Don't shuffle the order in which data points are visited for SGD or mini-batch SGD.

--max_iterations (-n) [int]
    Maximum number of iterations for L-BFGS (0 indicates no limit). Default value 100000.

--normalize (-N) [bool]
    Use a normalized starting point for optimization. Itis useful for when points are far apart, or when SGD is returning NaN.

--optimizer (-O) [string]
    Optimizer to use; 'amsgrad', 'bbsgd', 'sgd', or 'lbfgs'. Default value 'amsgrad'.

--passes (-p) [int]
    Maximum number of full passes over dataset for AMSGrad, BB_SGD and SGD. Default value 50. --print_accuracy (-P) [bool] Print accuracies on initial and transformed dataset

--rank (-A) [int]
    Rank of distance matrix to be optimized. Default value 0.

--regularization (-r) [double]
    Regularization for LMNN objective function Default value 0.5.

--seed (-s) [int]
    Random seed. If 0, 'std::time(NULL)' is used. Default value 0.

--step_size (-a) [double]
    Step size for AMSGrad, BB_SGD and SGD (alpha). Default value 0.01.

--tolerance (-t) [double]
    Maximum tolerance for termination of AMSGrad, BB_SGD, SGD or L-BFGS. Default value 1e-07. --update_interval (-R) [int] Number of iterations after which impostors need to be recalculated. Default value 1.

--verbose (-v) [bool]
    Display informational messages and the full list of parameters and timers at the end of execution.

--version (-V) [bool]
    Display the version of mlpack.

OPTIONAL OUTPUT OPTIONS

--centered_data_file (-c) [unknown]
    Output matrix for mean-centered dataset. --output_file (-o) [unknown] Output matrix for learned distance matrix.

--transformed_data_file (-D) [unknown]
    Output matrix for transformed dataset.

ADDITIONAL INFORMATION

For further information, including relevant papers, citations, and theory, consult the documentation found at http://www.mlpack.org or included with your distribution of mlpack.