# Which software is appropriate to integrate radial velocity with respect to time [closed]

I'm a high school student and currently I'm trying to use Baade-Wesselink method to independently derive period-luminosity relation of Cepheid variables. I noticed that to get the linear radius variation of a Cepheid, I need to integrate its radial velocity over its period.

The problem is, I don't know which program/software I should use to plot the best-fit line going through the points of the raw data of radial velocity over the phase. Even more, the thing is I need to integrate that best-fit line and plot the integrated curve as well.

Can anybody recommend good software that I can use?

(I've tried the integration with a program called Logger Pro but it was not successful. )

• Sounds like you want some sort of programming language that can handle this like Mathematica, R, Python, Matlab, etc. There are numerous choices. It just depends on which one you have access to and are comfortable learning. Aug 10 '16 at 19:32
• I agree, you will probably have to program it yourself. I don't know Matlab or R, but for python there's the astropy package that might have some building blocks for you to get started, so you won't have to do everything from scratch. From a quick look, it has model fitting and ploting tools.
– Alex
Aug 11 '16 at 8:14
• Use Simpson's rule or the Trapezium rule. Could be trivially done in a spreadsheet. Aug 18 '16 at 22:44
• I'm voting to close this question as off-topic because it isn't about astronomy, it is about numerical methods. Aug 19 '16 at 8:01
• I'm voting to close this question as off-topic because this question belongs on the Software Recommendations Stack Exchange. Aug 22 '16 at 14:04

If you know the period, $P$, and you know the $v$ AND if you know the theoretical relationship between them $v = f(p)$ then you can use linear least squares to compute the adjustable parameters of $f(p)$ by plotting $v$ (measured) vs $v$(calculated).
Any 'best fit' equation is able to interpolate values of $v$ so all you need to divide up the period into small intervals and approximate the area under the curve using its two end-points (it is rarely necessary to use parabolic fits that also use the mid-points of those small intervals).