set term svg fsize 18 background rgb "white"
set title "Logarithm of gamma-function lngamma(x)
set key bottom right
set tics out
set grid
set xzeroaxis
set yzeroaxis
set xlabel "x"
set ylabel "y"
set log x
set log y
ls(z)=z*log(z)-z-0.5*log(z/2*pi)
set out "LnGamma.svg"
plot [][] \
 "out.lngamma.txt" with lines title "lngamma(x)"\
,"out.lngamma.txt" using ($1):(ls($1))\
  with lines title "Stirling formula"