NEED FILES:  rw.f90 drandom.f90 rw.gpl average histogram
 only the first time give appropriate execute permissions:
 > chmod a+x average histogram


 > gfortran rw.f90 drandom.f90 -o rw
 > ./rw
 Usage: ./rw  <Nwalk> <Nstep>
 > ./rw  100      10000
gnuplot> set term wxt enha
gnuplot> plot "<awk '$1==1{print $2,$3}' data" w l
gnuplot> plot "dataR" u 2 w l t "R^2"
gnuplot> plot "dataR" u 3 w l t "x","dataR" u 4 w l t "y"
gnuplot> plot "dataR" u 5 w l t "n"
gnuplot> load "rw.gpl"
gnuplot> unset arrow;set size nosquare;set xrange [*:*];set yrange [*:*]

 Now compute some numbers:
> awk '{print $2}' dataR | ./average
> rm dataRN
> foreach n ( 10 50 100 500 1000 2000 4000 6000 8000 10000)
foreach? ./rw 10000 $n
foreach?  awk '{print $2}' dataR | ./average | awk -v n=$n '{print n,$0}' >>dataRN
foreach? echo $n
foreach? end
gnuplot> plot      "dataRN" u 1:2:4 w e
gnuplot> fit a*x+b "dataRN" u 1:2:4 via a,b
gnuplot> plot      "dataRN" u 1:2:4 w e,a*x+b