* compute psum
.control
let sj=0
while sj lt ndim
   let idx=0
   let sum=0 
   while idx lt mpts
   	 let xtmp=p[idx]
   	 let sum=sum+xtmp[sj]
   	 let idx=idx+1
   end
let psum[sj]=sum
let sj=sj+1
end
.endc

