factorization

For now only strings are accepted as the measures parameter in GridSearchCV, RandomizedSearchCV, and cross_validate. It's thus impossible to use those with measures that take specific parameters as input (e.g. #156 ), or to use custom measures.

We should then accept callables in addition to strings.

Each callable should only take the predictions parameter. In order to handle measur

It may be fun to extend Math.NumberTheory.Moduli.Jacobi to cover not only quadratic reciprocity, but cubic as well.

Quadratic reciprocity symbol or [Jacobi symbol](https://github.com/cartazio/arithmoi/blo

The FUN argument in comboGeneral() and similar RcppAlgos functions could be more useful if the user is allowed to provide the expected value, similar to vapply(). Currently, a list is allocated which can take up a lot of memory.

library(RcppAlgos)

ans = comboGeneral(15L, 3L, FUN = sum)
object.size(ans)
#> 29168 bytes
object.size(unlist(ans, use.names = FALS

a user might want to represent and evaluate multiple polynomials (different coefficients) with the same properties.
This is useful e.g. for gradients (= partial derivative polynomial for each dimension)!
add support for 2D coefficient arrays and adjust Numba jit compilation.
then the gradient can be returned as a single polynomial with the same exponents but 2D coefficients or multiple distinct