data{ // n: number of observations int n ; // x: continuous variable whose influence on y we're modelling as a GP real x[n] ; real pvn_ ; real lengthscale_ ; int sample_pvn ; int sample_lengthscale ; } transformed data{ real max_dist = max(x)-min(x); real min_dist = max_dist ; for(i_n in 1:(n-1)){ for(j_n in (i_n+1):n){ real dist = fabs(x[i_n]-x[j_n]) ; if(dist