How to send specific conditions to lsqcurvefit?

Hi, I have a experimental data fitting code given below. In this code from the differential equation (line 30), the 'lsqcurvefit' function (line 12) giving B(1) and B(2) estimation after fitting. From the theory, I know B(1)>B(2). I am just wondering, is there a way to send this condition into the function 'lsqcurvefit'?

Thanks

clear all, close all,  clc
HighVacData = xlsread('RawData','Sheet1','A2:B1603');% loading raw data from excel file
Timeall = HighVacData(:,1);
Sdataall = HighVacData(:,2);
Time = 0:1:11244.3353200000;
TimeC = Time.';

%parameter estimation (units per ns)
B0 = [2.96e-02,1.45e-3]; %sequence [k_rs]
lb = [0,0];% lower bound estimation
options = optimset('Algorithm', 'trust-region-reflective');   
[B,Rsdnrm,Rsd,ExFlg,OptmInfo,Lmda,Jmat] = lsqcurvefit(@ComGenUQFit,B0,Timeall,Sdataall,lb,[],options);%sending data for fitting
F = ComGenUQFit(B,TimeC);% fitted data saving

figure(1)
plot(Timeall,Sdataall,'bo')%raw data
hold on
plot(TimeC,F,'r','linewidth',2)%fit data
grid on
grid minor
xlabel('Time [ns]');
ylabel('Singlet');
legend('Experimental Data','Fit');
set(gca,'xscale','log')
set(gca,'yscale','log')

function S = ComGenUQFit(B,TimeC)% function for fitting
IC_ns = 11000;
  function dotn = Mat (TimeC,n)
     dotn(1) = -B(1)*n(1)-B(2)*n(1)^2;% equation for singlet Population
  end
[TimeC,dotnsolve] = ode45(@Mat,TimeC,IC);% calling ODE solver
S = dotnsolve(:,1);
end

Answer 1

[Bruno Luong]

Change you variable b to

c = [b(1), b(2)-b(1)]

meaning

b = [c(1), c(1)+c(2)]

Make lsqcurvefit works on c, with the constraint c(2)>=0 by seeting lb = [0; 0].

[Monirul Hasan]

Hey Bruno, I have tried to imply your suggestion. It is showing me an error "Undefined function or variable 'b'." Please let me know how to fix it. Also I have added a sample data file with this reply, please fill free to run the code with it. Thanks for your supports :)

[Bruno Luong]

Show you code modified.

I don't read xlsx sheet.

[Monirul Hasan]

I runned the code with your added lines (from comment 1), unfortunately it showing an error message. Please let me know how to fix it. Cheers.