gnuplot 用の記述
#
# van der Waals の状態方程式を
# 臨界点での温度と体積で規格化する。
#
# パラメタ
#
N = 1.0
RTc = 1.0
Vc = 1.0
a = 9.0*RTc*Vc/(8.0*N)
b = Vc/(3.0*N)
set yrange [0:1]
set xrange [0.4:5]
#
# 状態方程式 PR:実在気体 PI:理想気体
#
PR(V,RT) = N*RT/(V-b*N) - a*N**2/V**2
PI(V,RT) = N*RT/V
#
# 確認のため表示
# ( gnuplot で整数の割り算には注意。truncation が起こる)
#
print 1/3
print PR(1,1)
#
# X11
#
set term x11 0
plot PR(x,2), PR(x,1.5), PR(x,1.2), PR(x,1.1), PR(x,1.0), PR(x,0.90)
set term x11 1
plot PI(x,2), PI(x,1.5), PI(x,1.2), PI(x,1.1), PI(x,1.0), PI(x,0.90)
#
# gif
#
# set term gif small x808080 x909090 xA0A0A0 xB0B0B0 xC0C0C0 xD0D0D0 ; set output "VanDerWaals_PR.gif"
set term gif small; set output "VanDerWaals_PR.gif"
plot PR(x,2), PR(x,1.5), PR(x,1.2), PR(x,1.1), PR(x,1.0), PR(x,0.90)
set term gif small; set output "VanDerWaals_PI.gif"
plot PI(x,2), PI(x,1.5), PI(x,1.2), PI(x,1.1), PI(x,1.0), PI(x,0.90)
quit