Hello,
Would you please tell us the expression of your fitting function?
To follow the procedure of FittingWithBessel step by step is recommended:
http://www.originlab.com/doc/Tutorials/Fitting-Special-NAG
and here I provide a simple example for fitting with Airy for comparison
static NagError fail1;
y= A * (s17ahc(x,&fail1))+B;
if(fail1.code !=NE_NOERROR)
printf("%s\n",fail1.message);
for s17ahc and other Airy function, please refer to page below:
http://www.originlab.com/doc/LabTalk/ref/Approximations-of-Special-Functions-from-NAG
Best regards,
Jason Zhao
OriginLab Tech Service