"""This script makes a plot of the constant-L approximation
for the saturation vapor pressure for water, switching
from sublimation to vaporization latent heat at the triple point
"""

#Updated 10/31/2011.
#    Eliminated unneeded import of Numeric
#    Added comments related to using a gas object as an argument
#    Added axis labels
#Updates 11/12/2013: Shortened Labels of ice vs. liquid curves


#Data on section of text which this script is associated with
#**ToDo: Chapter and Figure references can be given in terms of
#LaTeX labels, which can then be turned into numbers using
#information in the .aux files LaTeX produces. This isn't so
#necessary for the Chapter refs, which won't change much, but
#it would be useful for the Figure refs.
Chapter = '2.**'
Figure = '**'
#

import phys
from ClimateUtilities import *
#

stuff = phys.water # Put your favorite substance here

#Set up a list of temperatures
Tlist = [200. + i for i in range(121)]

#Make empty lists to hold results of the three calculations
psatw = []
psati = []

#Compute the three saturation vapor pressures by looping
#over the temperatures in the list. Append the results
#to the appropriate lists.
#
#Note that instead of passing
#the thermodynamic properties as three separate arguments
#to phys.satvps_function, you could instead just use the
#gas object as the argument, as in
#satvps = phys.satvps_function(stuff)
#However, by default this uses the sublimation latent heat
#for temperature below the triple point and the vaporization
#latent heat above the triple point (which is usually what you
#want). Here, we want to illustrate the difference between vapor
#pressure over ice and over liquid, so we set the latent heat
#explicitly to the one we want in each case.  An alternate
#way to do this is to use a gas object as argument, but to specify
#which latent heat you want with the optional second argument, e.g.
#satvps_w = phys.satvps_function(stuff,'liquid')
#satvps_i = phys.satvps_function(stuff,'ice')
#
satvps_w = phys.satvps_function(
    stuff.TriplePointT,stuff.TriplePointP,stuff.MolecularWeight,stuff.L_vaporization)
satvps_i = phys.satvps_function(
    stuff.TriplePointT,stuff.TriplePointP,stuff.MolecularWeight,stuff.L_sublimation)
for T in Tlist:
    psatw.append(satvps_w(T)) #Exponential form based on L for water
    psati.append(satvps_i(T)) #Exponential form based on L for ice


#Put the results in a data structure for plotting
c = Curve()
c.addCurve(Tlist,'T','Temperature')
c.addCurve(psatw,'ps_w','Const L (liquid)')
c.addCurve(psati,'ps_i','Const. L (ice)')

#
# Set the plotting options. We use a logarithmic axis because the saturation
# vapor pressure varies over such a great range
c.YlogAxis = True
c.Xlabel = 'Temperature (K)'
c.Ylabel = 'Pressure (Pa)'
c.PlotTitle = 'Saturation Vapor Pressure for '+stuff.name

#Do the plot. 
plot(c)
#
#Write out to file
c.dump()