rlba_norm, only slightly faster than maker, calls C++
function directly.
rlba_norm(n, A, b, mean_v, sd_v, t0, st0, posdrift)is the numbers of observation.
start point upper bound, a vector of a scalar.
decision threshold, a vector or a scalar.
mean drift rate vector
standard deviation of drift rate vector
nondecision time, a vector.
nondecision time variation, a vector.
if exclude negative drift rates
a n x 2 matrix of RTs (first column) and responses (second column).