Fast computation of some matrices useful in statistics

Yet another R package for matrices. It contains a small set of functions to fast computation of some matrices and operations useful in statistics.

Latest release (September 18, 2020) of **fastmatrix** package have implemented the following functions:

- Array multiplication (see for instance, Appendix A of Wei, 1998).
- C version of the Kronecker product which is slightly faster than the built in R base.
- Column-equilibration for rectangular matrices.
- Covariance matrix estimation using the Mean Square Successive (MSSD) method.
- Estimation of the weighted mean and covariance matrix using an online algorithm (Clarke, 1971).
- Fast computation of Hadamard product using unrolled loops.
- Inner products and norms for matrices.
- Interface to
**C code callable by another C code**from other R packages. - Lp norms for vectors.
- Mahalanobis distances, checking if the covariance is a positive definite matrix.
- Operations envolving the commutation matrix, with minimum requeriments of storage.
- Operations envolving the duplication matrix, with minimum requeriments of storage.
- Operations envolving the symmetrizer matrix, with minimum requeriments of storage.
- Ordinary least-squares (OLS) using several methods: Cholesky, QR decomposition, singular value decomposition, and the Sweep operator. This provides an alternative to extend the procedures available in OLS.
- Power method to compute the dominant eigenvalue and its associated eigenvector.
- Procedures for the LU factorization of square matrices.
- Routines to compute measures of multivariate skewness and kurtosis proposed by Mardia (1970).
- Sherman-Morrison formula.
- Sweep operator for symmetric matrices.
- vec and vech operators to handle rectangular and square matrices.

Our plan in the near future is the implementation of functions to handle:

- Elimination matrices.
- Some special matrices and operations arising in numerical analysis.

Latest binaries and sources for **fastmatrix** are availables from CRAN package repository

- fastmatrix_0.3.tar.gz - Package sources
- fastmatrix_0.2-3571.zip - Windows binaries (R-release)
- fastmatrix_0.2-3571.tgz - Mac OS binaries (R-release)
- fastmatrix.pdf - Reference Manual

To install this package, start R and enter:

```
install.packages("fastmatrix")
```

Alternatively, you can download the source as a tarball or as a zip file. Unpack this file (thereby creating a directory named, fastmatrix) and install the package source by executing (at the console prompt)

```
R CMD INSTALL fastmatrix
```

Next, you can load the package by using the command: `library(fastmatrix)`

Please report any bugs/suggestions/improvements to Felipe Osorio, Universidad Tecnica Federico Santa Maria. If you find these routines useful or not then please let me know. Also, acknowledgement of the use of the routines is appreciated.

Osorio, F., Ogueda, A. (2020). fastmatrix: Fast computation of some matrices useful in statistics. R package version 0.2-3571. URL: faosorios.github.io/fastmatrix

Felipe Osorio is an Assistant Professor at Department of Mathematics, Universidad Tecnica Federico Santa Maria, Chile.

- Webpage: fosorios.mat.utfsm.cl
- Email: felipe.osorios [AT] usm.cl

Alonso Ogueda is a student of the Master of Mathematics offered by the Department of Mathematics, Universidad Tecnica Federico Santa Maria, Chile.

- Github: github.com/aoguedao