MATLAB: Fit options in a parfor loop

bugfitfitoptionsParallel Computing Toolbox

I am performing a fit of data multiple times using a loop. When I use a "for" loop, everything works as expected. However, if I use a "parfor" loop, I get an error. If I remove the fit options (fo), then the parfor loop works as expected. Does anyone know why the parfor loop generates an error when I specify the fit method using the fitoptions?
% Generate some data
Npts = 50;
Ntime = 10;
tau = 10;
x = repmat( (1:Npts)',1,Ntime);
y = exp(-x/tau) + (rand(Npts,Ntime)-0.5)/10;
% Plot the data
figure;
plot(x(:,1),y(:,1),'-o')
title('Data for first time step')
% Fit options
ft = fittype('exp1');
fo = fitoptions( 'Method', 'NonlinearLeastSquares' );
% Pre-allocate the decay constant, tau
tau = NaN(1,Ntime);
parfor q = 1:Ntime
        
    % Perform the exponential fit at time step q
    fitresult = fit( x(:,q), y(:,q), ft, fo);
    
    % Save the decay constant, tau
    tau(q) = -1/fitresult.b;
    
end

Best Answer

Thanks all for the support. I ended up setting the fit method as a character string outside of the loop (near the top, where I usually keep such "manual/hard-coded" values), and then constructing the fitoptions inside the parfor loop. 
% Generate some data
Npts = 50;
Ntime = 10;
tau = 10;
x = repmat( (1:Npts)',1,Ntime);
y = exp(-x/tau) + (rand(Npts,Ntime)-0.5)/10;
% Plot the data
figure;
plot(x(:,1),y(:,1),'-o')
title('Data for first time step')
% Fit options
fiteqn = 'exp1';
fitmethod  = 'NonlinearLeastSquares';
% Pre-allocate the decay constant, tau
tau = NaN(1,Ntime);
parfor q = 1:Ntime
        
    % Perform the exponential fit at time step q
    ft = fittype(fiteqn);
    fo = fitoptions( 'Method', fitmethod);
    fitresult = fit( x(:,q), y(:,q), ft, fo);
    
    % Save the decay constant, tau
    tau(q) = -1/fitresult.b;
    
end
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