function for creating a Helmert matrix in Stan

helmert.stan

functions {
matrix helmert(int levels) {
  matrix[levels, levels - 1] m = rep_matrix(-1, levels, levels - 1);
  real k = 0;
  for(j in 1:(levels - 1))
    for(i in 1:levels)
      if(j <= i - 2) 
        m[i, j] = 0;
      else if(j == i - 1) {
        k = k + 1;
        m[i, j] = k;
      }
  return m;    
}   
}
data { 
}
parameters {
}
model {
}