>> TGS_phase_analysis('Fe_single_crystal-2019-06-29-06.40um-90degrees#3-POS-1.txt','Fe_single_crystal-2019-06-29-06.40um-90degrees#3-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 =        0.12  (0.1185, 0.1215)
       k =   2.252e-05  (2.234e-05, 2.27e-05)
       beta =   3.908e-06  (3.368e-06, 4.447e-06)
       B =     0.02436  (0.02414, 0.02459)
       p =       2.388  (2.382, 2.395)
       t =   2.783e-08  (2.746e-08, 2.82e-08)
       D =  -0.0006332  (-0.0006952, -0.0005712)
     Problem parameters:
       q =   9.817e+05
       start_time =     1.2e-09
       peak_freq =   4.553e+08

ans =

   4.5526e+08