Implement Curve Fitting Code in Simulink block

Hello,

I am trying to implement some code, which was generated in the Curve Fitting Tool, into my Simulink model with a Matlab function block. The script fits a surface on three inputs. With the other two inputs I want to evaluate a point on the calculated surface. I already added some code to make this script work, but something is still missing. I think, that it has something to do with a proper declaration of the fitresult variable. The code below gives the error message "MATLAB expression 'fit' is not numeric.".

 function force_n  = fcn(travel, pressure, force, travel_n, pressure_n)

%  Create a fit.
%
%  Data for 'airspring' fit:
%      X Input : travel
%      Y Input : pressure
%      Z Output: force
%  Output:
%      fitresult : a fit object representing the fit.
%      gof : structure with goodness-of fit info.
%
%  See also FIT, CFIT, SFIT.

%%own code
coder.extrinsic('prepareSurfaceData'); 
coder.extrinsic('fit');
fitresult = coder.nullcopy(zeros(size(1)));
force_n = 0

Auto-generated by MATLAB on 20-Nov-2016 20:35:21

 % Fit: 'airspring'.
 [xData, yData, zData] = prepareSurfaceData( travel, pressure, force );

 % Set up fittype and options.
 ft = 'linearinterp';

 % Fit model to data.
 fitresult = fit( [xData, yData], zData, ft, 'Normalize', 'on' );

 %%output data
 force_n = feval(fitresult,travel_n,pressure_n)
 %force_n = fitresult(travel_n,pressure_n)

If someone wants to test the code I've attached a model with the code block and the input data. It would be great, if anyone has a solution or an idea how to solve this problem!

Thomas

[Rohan Gupta]

Even I am facing the same problem. Getting same error 'fit is not numeric'. Do let me know if you have found the solution. It would be helpful.