>> TGS_phase_analysis('Cr_single_crystal-2019-06-27-06.40um-10degrees-POS-1.txt','Cr_single_crystal-2019-06-27-06.40um-10degrees-NEG-1.txt',6.4,1)

f2 = 

     General model:
     f2(x) = A.*(erfc(q*sqrt(k*(x+start_time)))-beta*exp(-q^2*k*(x+start_time)
                    )./sqrt((x+start_time)))+B.*sin(2*pi*(peak_freq)*(x+
                    start_time)+p)*exp(-(x+start_time)/t)+D
     Coefficients (with 95% confidence bounds):
       A =     0.02083  (0.02013, 0.02152)
       k =   2.604e-05  (2.544e-05, 2.663e-05)
       beta =    2.83e-06  (1.546e-06, 4.114e-06)
       B =     0.01066  (0.01053, 0.01079)
       p =      -2.091  (-2.1, -2.082)
       t =   2.382e-08  (2.338e-08, 2.427e-08)
       D =   0.0004743  (0.0004444, 0.0005043)
     Problem parameters:
       q =   9.817e+05
       start_time =       7e-10
       peak_freq =   5.499e+08

ans =

   5.4991e+08