Add matrix multiplication operator for torch_tensor

[caiohamamura]

A very common operation we need to perform when using tensors is the matrix multiplication. This is just a generic cast of %*% operator to torch_matmul.

#' @export
`%*%.torch_tensor` <- function(e1, e2) {
  if (!is_torch_tensor(e2)) {
    e2 <- torch_tensor(e2, device = e1$device)
  }
  torch_matmul(e1, e2)
}

[dfalbel]

Muito obrigado @caiohamamura !

We probably want something like @rawNamespace if (getRversion() >= "4.3.0") S3method("%*%", torch_tensor) instead of #' @export to support older R versions.

[caiohamamura]

Do you want me to make that change? Then maybe that should also be done for every method then? Because all other operators are using only #' @export too.

[dfalbel]

I can do it! I don't think we need for all methods. %*% is a special case because it has been recenttly introduced as an S3 generic in R 4.3.

https://cran.r-project.org/doc/manuals/r-release/NEWS.html

The matrix multiply operator %*% is now an S3 generic, belonging to new group generic matrixOps. From Tomasz Kalinowski's contribution in PR#18483.