Find the marker index corresponding to the peak of the pleiotropy trace in a tibble where the last column contains log likelihood values and the first d columns contain marker ids
a (d+1) column tibble with first d columns containing marker ids and the last containing log likelihood values. Typically this is the output from `scan_pvl`.
positive integer, from the two-dimensional scan, that indicates where the scan started on the chromosome
positive integer indicating marker index for maximum value of log lik under pleiotropy