[R] fitting a gaussian to some x,y data
Michael Koppelman
michael at isis.spa.umn.edu
Fri Aug 25 21:35:31 CEST 2006
Thank you. Yes, I do feel that I am under-qualified to even ask
questions of y'all. Plus I'm an astronomer, which doesn't help! ;)
I'll try again.
I have two columns of data, the first column (x) is a distance (or
length or separation) and the second column (y) is a flux (or number
of counts or brightness) at that distance. Thus, when you plot y vs.
x you get a spatial profile which shows how bright this thing is as a
function of position. (See the small, attached PNG file. You can see
there is a vague gaussian shape to the data.) This is measured data
from a bizarre technique which yields data that is not evenly-spaced
in x and it does not represent a pure mathematical function (i.e. it
is not a point spread function or something like that), it represents
the actual, non-uniform shape of an astronomical object. We are
making the assumption that the shape of this object can be roughly
represented with a gaussian.
I want to fit a gaussian to this with the purpose of determining
systematically the "center" of the normal-like shape of the spatial
feature. I have successfully done so in R with a polynomial but I
can't figure out how to do it with a gaussian.
Does that make sense?
Thanks!
Michael
On Aug 25, 2006, at 2:04 PM, MARK LEEDS wrote:
> hi : i'm not clear on what you mean but someone else might be ? if you
> say ( x,y), then it sounds like you are talking about a bivariate
> normal
> distribution. to fit a regular one dimensional gaussian distribution,
> you can't have 2 dimensional data. i honestly don't mean to sound
> rude but
> i think you should explain what you want to do more clearly
> because I don't think
> I am the only one that will be confused by what you said.
> send out a clearer email and you will get quite a response because
> there are a lot of really smart people ( compared to me ) on this
> list that love to help.
> it's an amazing list in that sense.
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