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Re: polyfit weirdness
From: |
Miquel Cabanas |
Subject: |
Re: polyfit weirdness |
Date: |
Wed, 12 Feb 2003 13:57:23 +0100 |
User-agent: |
Mutt/1.3.28i |
hi,
On Tue, Feb 11, 2003 at 02:08:37AM -0600, Scott Lamb wrote:
>
> So first I'm calling polyfit to get the trendline:
>
> l1 = 1e-9 * [ 578.45 545.88 435.87 404.71 365.26 ]
> v1 = [ 0.66 0.79 1.40 1.58 1.92 ]
> f1 = 299792458 ./ l1
> [p1,cv1] = polyfit(f1,v1,1)
>
> ...and it doesn't return what I'd expect at all:
I think we can narrow the problem to be related to the
left-division in polyfit, could you try running (this is
what polyfit does),
n = 1;
l = 5;
x = [ 5.1827e+14 5.4919e+14 6.8780e+14 7.4076e+14 ...
8.2076e+14 ]';
y = [ 0.66000 0.79000 1.40000 1.58000 1.92000 ]';
X = (x * ones (1, n+1)) .^ (ones (l, 1) * (0 : n));
p = X \ y;
yf = X * p;
In my working Octave I get
p =
-1.4948e+00
4.1680e-15
and (estimated y-values)
yf =
0.66529
0.79416
1.37188
1.59262
1.92605
Also, what are eps, realmax and realmin in your versions? Again,
mines are,
eps = 2.2204e-16
realmax = 1.7977e+308
realmin = 2.2251e-308
Miquel
--
Miquel E Cabanas ------------------------------------------------------
SeRMN, Universitat Autonoma de Barcelona (address@hidden)
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Re: polyfit weirdness,
Miquel Cabanas <=