Finds the nearest neighbours of a marker with LOD scores > 0.
get.nearest.informative(loci, lodmap)
Scalar indicating a marker number
Symmetric matrix of pairwise LOD scores
A vector of length 1 or 2 containing the rank of the nearest informative markers.
The columns and rows of the matrix should be in the order corresponding to the estimated map order. The function then returns the ranks of first markers to the left and right of the marker of interest with non-zero lod scores.