>> TGS_phase_analysis('Cr_single_crystal-2019-06-30-06.40um-35degrees#3-POS-1.txt','Cr_single_crystal-2019-06-30-06.40um-35degrees#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 =     0.01922  (0.01906, 0.01938)
       k =   2.653e-05  (2.612e-05, 2.693e-05)
       beta =   5.908e-10  (fixed at bound)
       B =    0.009363  (0.00924, 0.009486)
       p =       3.114  (3.105, 3.124)
       t =   2.564e-08  (2.513e-08, 2.614e-08)
       D =   0.0005055  (0.0004792, 0.0005317)
     Problem parameters:
       q =   9.817e+05
       start_time =       9e-10
       peak_freq =   5.469e+08
Bad fit for:Cr_single_crystal-2019-06-30-06.40um-35degrees#3-POS-1.txt~re: beta

ans =

   5.4687e+08