Central Charge

# SCRIPT TO EXTRACT CENTRAL CHARGE AFTER FIT! 
import os

#Eiji code
def fit_and_extract(filename):
	pplot = open("gnuplot.dat", "w")
	pplot.write("a=1\nb=1\nc=1\nf(x)=d-(c*pi)/(6*x*x)\nfit f(x) \""+filename+"\" via c,d") 

	pplot.close()
	os.system("gnuplot gnuplot.dat ; tail fit.log -n15 > fit2.log")
    
    # VERY IMPOTANT THING!!!!!!!!
    # in the same directory where is the python file one needs to put the awk.awk file!!!!!!!!!!!!
    # This also applies for Ipython notebook! (put awk.awk file where the notebook file is saved!)
    
	f=os.popen("awk -f awk.awk fit2.log")
	for line in f:
		a=float(line.split()[0])
	return a

# loop over all different exchange parameters J (in this example 0.2<J<0.6 )
for k in range(0,30):
    

    exchange_parameter_value = 0.2 + k*0.04 #this will read from data files created with the main script
    print "Exchange constant:",exchange_parameter_value
    
    
    # open file to write
    c = ''.join([str('big_daddy'),str(exchange_parameter_value),str('.txt')])
    f = open(c,'w')
    
    
    count = 0
   # ---Now we read specific lines and extract the central charge for them ---
    for i in range(3,11): #here the range needs to be adapted to the number of lattice sizes we calculated
        first = i
        second = i + 2
        count = count + 1
        
        filee = "<(sed -n '"+str(first)+","+str(second)+"p' ""koji"+str(exchange_parameter_value)+".txt)"
        c = fit_and_extract(filee) # central charge value
        
        ww = ' '.join([str(count),str(c)])
        f.write(str(ww))
        f.write('\n')
        
        print c
        
    f.close()