This code implements the algorithms used in the experiment of the following papers in C/C++ and MPI: Lee, Ching-pei, Lim, Cong Han, Wright, Stephen J. A Distributed Quasi-Newton Algorithm for Primal and Dual Regularized Empirical Risk Minimization. Technical Report, 2019.

Lee, Ching-pei, Lim, Cong Han, Wright, Stephen J. A Distributed Quasi-Newton Algorithm for Empirical Risk Minimization with Nonsmooth Regularization. The 24th ACM SIGKDD International Conference on Knowledge Discovery and Data Mining, 2018.

In additional to our algorithm, the following algorithms are also implemented.

• OWLQN
• SPARSA
• BDA (with Catalyst)
• ADN

To compile the code, you will need to install g++ and an implementation of MPI. You will need to list the machines being used in a separate file, and make sure they are directly accessible through ssh. Additionally the code depends on the BLAS and LAPACK libraries.

The code split.py, borrowed from MPI-LIBLINEAR, partition the data and distribted the segments to the designated machines. Then the program ./train solves the optimization problem to obtain a model.

Solvers 0-2 solve the L1-regularized logistic regression problem

min_{w} |w|1 + C \sum{i=1}^n \log(1 + \exp(- y_i w^T x_i))

with a user-specified parameter C > 0.

Solvers 3-6 solve the dual problem of the L2-regularized squared-hinge loss problem The primal problem is:

min_{w} |w|2^2/2 + C \sum{i=1}^n \max(0,1 - y_i w^T x_i),

with a user-specified parameter C > 0, and the dual problem is:

min_{\alpha \geq 0} |\sum_{i=1}^l \alpha_i x_i y_i|2^2 / 2 + \sum{i=1}^l \alpha_i^2 / (4C) - \sum_{i=1}^l \alpha_i.