curve fitting gives input, at the output

[alican]

Hi everybody, i am having a problem at curve fitting function,

i take at output, what i give as input, where do i make mistake?

at example i give 4 values, if i enter 6 values it works, but i need to do it with 4 values.

any ideas?

thanks

[TiTou]

take a look a the help topic about the non-linear fitting VI :

Apparently what you did was creating a constant on the f(x,a) termanial, this then causes an error because the VI is expecting you to create a VI from a template. You either have to create that VI or use a different fitting method.

Hope this helps

[alican]

Hi, thanks for ur answer

I did it with nonlinear curve fitting function, but there should be some mistakes, still doesnt working?

[alican]

Bye the way, i dont know how to decide initial parameters, can anybody help me with that?

thanks

[TiTou]

What's wrong? it works fine for me... what error are you getting?

Of course you need to input an array containing 3 values in "initial parameters" for the initial values of a1, a2 and a3.

Hope this helps

[alican]

thanks, i didnt put 3 values for it, i will try it like that. 

and how can i determine, which values should i write as initial values?

[alican]

i entered 3 value as u said, now i dont get any error, but output is same as input. function doesnt make any curve.

if u got curve, can u share ur initial parameters with me

[johnsold]

Please include your data.  What values are you using for Array and Initial Parameters?  With only 4 data points you may have a system which either matches perfectly to a the curve or which cannot be matched by a second order curve.

For example an input of 0,3,3,0 with initial = 2,2,2 produces -6.8E-17, 3, 3, 1.7E-15 which plots identically to the input.

Lynn

[altenbach]

Your function is a simple quadratic polynomial, so you should use the general polynomial fit function instead. Don't overcomplicate things 😄

[alican]

sorry, i thought datas will be visible if i upload program.

i used as input

0.005

-0.05

-0.05

-0.005

as initial values, i have no idea what should i write, which value:/.

i need to do it with 4 data, 

thank you