| Re: Principal Componets Analysis [message #94519 is a reply to message #55733] |
Tue, 20 June 2017 04:39   |
rjp23
Messages: 97
Registered: June 2010
|
Member |
|
|
This is a bit of an extreme bump but I've just stumbled upon this and need to do something similar.
The disclaimer here (http://www.idlcoyote.com/code_tips/pca.html) bothers me a bit: [Editor Note: After writing an article on EOF Analysis, which is identical to Principal Component Analysis, I have a feeling this section of the article might be slightly misleading. Let's just say, I wouldn't do it this way if I were doing the analysis again now.]
I don't know if David's still around but could someone elaborate a bit more on that? What's the issue with the article that'd be done differently?
Thanks
On Tuesday, September 4, 2007 at 1:33:37 AM UTC+1, David Fanning wrote:
> David Fanning writes:
>
>> Well, I'm ashamed to say, I had read part's of Mort's book
>> earlier in the week and found I needed, well, more remedial
>> help. Quite frankly, I didn't understand a word of it. :-(
>>
>> The Lindsay Smith tutorial, on the other hand, was crystal
>> clear (http://tinyurl.com/3aaeb6). So much so that I came
>> back to my office and wrote up the example in IDL, just
>> to see if I could follow it.
>
> Well, I'm back, this time with a spelling of "principal"
> that might even make this discussion of Principal Components
> Analysis (PCA) available to people who can spell correctly
> on Google searches. (And I have bookmarked the difference
> between "principle" as a fundamental truth or law, and
> "principal" as the first in rank, in my dictionary. How
> you get to be my age without knowing this is beyond me.)
>
> I've been pretty much obsessed with PCA for the past couple
> of weeks. For one thing, I felt badly about telling Mort
> I couldn't understand a word of his excellent book. (It
> does grow on you when you finally find yourself up to
> speed again on some of the mathematical notations.)
>
> Anyhow, I've wanted to understand this. Probably for the
> same reason I've been studying Spanish so diligently
> lately: it just seems like it might come in handy some
> day. Does anyone know if they use PCA in Costa Rica?
>
> PCA *is* fairly straightforward. At least after you
> understand it, it is. Getting there is something else.
> I suspect there are more of you out there like me who
> would appreciate a--shall we say--less mathematical
> approach to the subject.
>
> I found MUCH became clear after reading the above
> mentioned Lindsay Smith tutorial:
>
> http://tinyurl.com/3aaeb6
>
> But there were still a few unresolved problems for me.
> One of these was why there are two ways to do PCA in
> IDL, and why you don't get the same answer when you use
> them. I discovered, eventually, that you DO get the same
> answer, but this took me a whole lot longer to figure
> out than it probably should have.
>
> I also wanted to understand the use of PCA for images,
> so I looked into that a little bit, too.
>
> All this to say that I have written what I am calling
> a PCA Tutorial, although that is probably a lofty title
> for a piece of writing that is more like the blind leading
> the blind. :-)
>
> I would appreciate feedback on this from those of you
> who know a lot more about it than I do. I tried to let
> the Smith tutorial do the heavy theoretical lifting.
> What I wanted to know was how to do this in IDL. So that
> is the focus here. (I did find what I think is an error
> in the Smith tutorial, for what it is worth.)
>
> You can find the tutorial here:
>
> http://www.dfanning.com/code_tips/pca.html
>
> Any and all comments welcome.
>
> Cheers,
>
> David
>
> --
> David Fanning, Ph.D.
> Fanning Software Consulting, Inc.
> Coyote's Guide to IDL Programming: http://www.dfanning.com/
> Sepore ma de ni thui. ("Perhaps thou speakest truth.")
|
|
|
|
comp.lang.idl-pvwave archive
Members
Search
Help
Login
Home
