MATLAB: How to take R-Square value as a variable

cftoolcurveexponential curvefitfitting

I could take some a, b and c value of custom exponential equation.(F.a, F.b and F.c)
I'd like to compute R-square value to a loop to use as a threshold.
When I compute this, it shows several values including R-square. How can I take this value only to use a variable? 
A=readtable('R_square_practice.xlsx');
A=table2array(A);
t=A(:,1);      
b=A(:,2); 
initial=rand(1,3);
ft = fittype('a*exp(-x/b)+c');
F=fit(t,b,'StartPoint',initial(:,:));
[curve2,gof2] = fit(t,b,ft)
-----------------------------------------------------------------------------------
curve2 = 
     General model:
     curve2(x) = a*exp(-x/b)+c
     Coefficients (with 95% confidence bounds):
       a =        6749  (3683, 9814)
       b =       1.185  (-0.009564, 2.379)
       c =   4.581e+04  (4.518e+04, 4.643e+04)
gof2 = 
  struct with fields:
           sse: 5.4861e+07
       rsquare: 0.4751
           dfe: 25
    adjrsquare: 0.4331
          rmse: 1.4814e+03

Best Answer

If you mean you want to access the value of the rsquare field, you can do that as with any struct (see the line of code below). If this is not what you mean, please edit your question to clarify.
R2_value=gof2.rsquare;
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