comp.lang.idl-pvwave archive: archive » Best fit line for sinusoid

Home » Public Forums » archive » Best fit line for sinusoid

Show: Today's Messages :: Show Polls :: Message Navigator
E-mail to friend

Re: Best fit line for sinusoid [message #92015 is a reply to message #92010]

Wed, 30 September 2015 09:07

liam.steele
Messages: 13
Registered: September 2015

Junior Member

On Wednesday, 30 September 2015 15:23:01 UTC+1, liam....@gmx.co.uk wrote:
> Hi all,
>
> I was wondering if there was a 'simple' way to get IDL to plot a best fit line for a sinusoidally-varying data set. For example, say temperatures were recorded each hour for 5 days at a certain location, with each measurement having an error of 2 deg C. Then we would have something like:
>
> day = findgen(121)/24
> temp = 15 + 10*sin(10*!pi*findgen(121)/120) + 5*randomu(seed, 121)
> error = fltarr(121)+2
>
> Is it possible from these three arrays for IDL to work out and plot a best fit line? I have searched online, and can't really find what I'm looking for. (surprisingly I have never had to plot a best fit line to anything before!)
>
> Cheers,
>
> Liam

Thanks for the tips everyone. I've managed to get something which I think looks correct, so that's good! I'll add the error bar plot when I work on the real data. The code I used was this:

day = findgen(121)/24
temp = 15 + 10*sin(10*!pi*findgen(121)/120)+5*randomu(seed, 121)
error = fltarr(121)+2
meanval = mean(temp)

expr = 'P[0] + P[1]*sin(P[2]*2*!pi*findgen(P[3])/(P[3]-1) + P[4])'
start = [meanval, (max(temp)-min(temp))/2, 5., 121, 0.]

result = MPFITEXPR(expr, day, temp, error, start)
fitline = result[0] + result[1]*sin(result[2]*2*!pi*findgen(result[3])/(result[3]- 1) + result[4])

plot, day, temp, psym=sym(2)
oplot, day, fitline

Report message to a moderator

[Message index]

		Best fit line for sinusoid By: liam.steele on Wed, 30 September 2015 07:22
		Re: Best fit line for sinusoid By: David Fanning on Wed, 30 September 2015 07:37
		Re: Best fit line for sinusoid By: liam.steele on Wed, 30 September 2015 07:51
		Re: Best fit line for sinusoid By: chris_torrence@NOSPAM on Wed, 30 September 2015 08:19
		Re: Best fit line for sinusoid By: liam.steele on Wed, 30 September 2015 09:07

Previous Topic:	Job Posting: Computer Research Specialist / Research Software Engineer / University of Florida
Next Topic:	join

-=] Back to Top [=-

[ Syndicate this forum (XML) ] [

] [

]

Current Time: Wed Oct 08 11:35:30 PDT 2025

Total time taken to generate the page: 0.00435 seconds