MATLAB: Fit NonLinearLeastSquares to data and constrain curve to pass through point (0,1)

Curve Fitting ToolboxMATLAB and Simulink Student Suitenonlinear least squares regression

I have data I need to fit to an equation, which I can do, but I want the equation to pass through point (0,1).
The equation is an exponential y = a*exp(-x/b)+ c*exp(-x/d)+ e
Currently, this is my code:
f3 = fitoptions('Method','NonlinearLeastSquares','Startpoint',[1,100,1,100,1])
newrelax = fittype('q*exp(-x/r)+ s*exp(-x/t)+u','options',f3);
[h,gof] = fit(timeR,stressR,newrelax)
plot(h,timeR,stressR)
Thank you,
-Zach

Best Answer

You can use a “lsqlin” function from optimization toolbox. 
t=coeffvalues(h); 
C=[exp(-x/t(2)) exp(-x/t(4)) ones(size(x))]; 
D=y; 
A = []; % No inequality constraint 

B= []; % No inequality constraint 
%Set the specified points in C and D to find equality constraints Aeq, Beq..By substituting (0,1) they turned out to be 
Aeq =[1 1 1];Beq=[1]; 
l=lsqlin(C,D,A,B,Aeq,Beq);     %generates coefficients of the curve fitted passing through a specified point  
Plot(timeR,C*l);
Refer to the below link
https://www.mathworks.com/help/optim/ug/lsqlin.html
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