Fitting loose Data to a known curve

[Messi]

Hi everybody,

I come up with a curve fitting problem. Unfortunately, It's not a regular curve fitting application where a specific function is fitted to a set of data. More precisely I need the inverse operation because I would like to fit my data with least deviation error to a curve that I have. To put it in other words:
I have a curve that describes a fluid velocity profile over pipe diameter, i.e. velocity as a function of space. In my measurements I have a spectrum of velocities which now need to be adapted to this known velocity curve. That means I don't have a relation between measured velocity and space. Therefore I need to sort my velocity informations in space along the known curve in order to obtain a spacial allocation
of the measured velocities.
I didn't find a VI for such purpose. If somebody knows a solution in my case I would be very pleased!
Many thanks in advance!!

[chilly_charly]

May be we need to dig further into this.

What I understand is that you have v = f(x), where f is a known function. Then you have a series of v values and you want to find the corresponding x's.
So the problem is to find the inverse function of f, so that x = g(v). If g cannot be formally established, your problem becomes a root solving problem (zero), and you are looking for the x solution of f(x)-v = 0.
There are a number of vi's in LV to do this : seen in the "Analyze>Mathematics>Zeroes" subpalette...

Hope this helps. Give some feed back here !

CC

[Messi]

That's a good idea!! I will try on this way!!
Thank you very much for that hint, Chilly Charly!!

8-)
messi