Thang Nguyen Posted March 21, 2011 Report Share Posted March 21, 2011 Hi, I have a set of data which is in a shape of exponential rise function. I cannot find any fitting VI can fit this data set so I would like to build one. I know that my data set is Y = A - B*exp(-C*X). But I don't know how should I start to make my VI can find the fit automatically. I highly appreciate your time on reading and answering my questions. Best regards, Thang Quote Link to comment
crelf Posted March 21, 2011 Report Share Posted March 21, 2011 I assume Y is an array, but which of A, B and C are scalars/arrays? Quote Link to comment
Thang Nguyen Posted March 21, 2011 Author Report Share Posted March 21, 2011 Crelf : X is an arry Quote Link to comment
ShaunR Posted March 21, 2011 Report Share Posted March 21, 2011 Are using the "Base Package"? Quote Link to comment
mzu Posted March 22, 2011 Report Share Posted March 22, 2011 Are using the "Base Package"? This particular implementation of Exponential fit was known to have problems when data falls below 0. Use http://zone.ni.com/reference/en-XX/help/lv/71/gmath/Levenberg_Marquardt/ instead. I am not a great fan of express VIs, but potentially you can use Curve Fitting.vi express VI. Both require something more then base package. An overkill for such a simple problem, but you can also use Quote Link to comment
Thang Nguyen Posted March 22, 2011 Author Report Share Posted March 22, 2011 Hi, I tried with base package but it doesn't work in my case. I attach here the graph and data set. Thang TestFitData.txt Quote Link to comment
Thang Nguyen Posted March 22, 2011 Author Report Share Posted March 22, 2011 I found the nonlinear curve fitting VI and play with it, but by some reason it doesn't work. I attach it here so you may can try it. Select TestFitData.txt as source TestFitData.txt TestFit.vi Quote Link to comment
vugie Posted March 22, 2011 Report Share Posted March 22, 2011 I found the nonlinear curve fitting VI and play with it, but by some reason it doesn't work. I attach it here so you may can try it. Select TestFitData.txt as source Can't you just move the data to domain where expotential fitting works? Like this: Quote Link to comment
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