impute_variant_fast: Imputes a set of variants
In stephenbates19/digitaltwins: Causal inference for SNPs

Imputes the variants in a specified group, conditional on other variants, based on the recombination model. This is intented for use a subroutine of the conditional randomization test.

1 2	impute_variant_fast(x, p1, p2, group, d, fb_result = NULL, lambda = 0.012, epsilon = 1e-08, window_size = 200)

`x`	0-1 vector of length p. The observed haplotypes of the offspring.
`p1`	0-1 vector of length p. One of the parental haplotypes giving rise to `x`.
`p2`	0-1 vector of length p. The other parental haplotypes giving rise to `x`.
`group`	a subset of indices of 1:p. This subset of variants will be imputed.
`d`	numeric vector of length p. The genetic distance between variants
`lambda`	the recombination rate, in units of the vector d
`epsilon`	the pointwise mutation rate
`window_size`	when imputing the variants, look only at a window of this size surrounding the group g. A smaller window size leads to faster computation and avoids numerical issues.