Peter Hewitt schrieb:
> I have a few points on a graph, and would like a C++ function that
> calculates a best fit equation such as a n degree polynomial.
>
> Are there functions already available to do this, or any ideas how I would
> write one.
> I've checked on the web but can't seem to find anything useful.
>
> Thanks,
> Pete
>
>
I recommend you to use a special form of polynomial interpolation, the
"spline interpolation".
After understanding the mathematical background, it is relatively easy
to implement a spline function into a given computer language like C or
C++. Years ago I implemented it even in assembler for an embedded
real-time system with very restricted hardware ressources, later in C,
when RAM and EEPROM together with the 8/16-bit microcontroller become
cheaper.
http://de.wikipedia.org/wiki/Spline
http://de.wikipedia.org/wiki/Spline-Interpolation
http://en.wikipedia.org/wiki/Spline_%28mathematics%29
http://en.wikipedia.org/wiki/Spline_interpolation
If you are too lazy to implement it by your own, you could try to use
the GSL (GNU Scientific Library).
The GNU Scientific Library (GSL) is a numerical library for C and C++
programmers.
It is free software under the GNU General Public License.
The library provides a wide range of mathematical routines such as
interpolation, polynomials, random number generators, special functions
and least-squares fitting. There are over 1000 functions in total with
an extensive test suite.
http://www.gnu.org/software/gsl/
http://www.gnu.org/software/gsl/manual/html_node/
http://www.gnu.org/software/gsl/manual/html_node/Interpolation.html
Another possibility for your purpose could be Scilab / Scicos, an "open
source" scientific math package, IMHO written in C / C++ and its source
code free available. You could try to extract pieces of the source code
that you need.
http://en.wikipedia.org/wiki/Scilab
To try an example with your values (points in your graph) there is a
spline calculator, written in Java, that you could take a look at:
http://www.arndt-bruenner.de/mathe/scripts/kubspline.htm#rechner
I hope your German is better then my English ;-)
Gruß,
Werner Kitzmann
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