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## polyfit weirdness

**From**: |
Scott Lamb |

**Subject**: |
polyfit weirdness |

**Date**: |
Tue, 11 Feb 2003 02:08:37 -0600 |

**User-agent**: |
Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.0.1) Gecko/20020826 |

`I'm trying to use Octave (2.1.36, 2.1.44) for the first time. I want to
``put some data in, make a trendline, and make a graph with the raw data,
``trendline, trendline's formula, and correlation displayed, and attach
``them to a LaTeX document when I'm done. (The sort of thing I could do
``easily in Excel, but I want to learn a new open-source tool.)
`
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:
p1 =
1.9796e-15
2.8980e-30
cv1 =
1.0260 1.0872 1.3616 1.4664 1.6248

`cv1 should hold its computed (near-identical to v1) values, right? But
``they're not even close. Doing this in Excel gives a slope of 4.17e-15
``and R^2 = .999. So these definitely aren't right. What am I doing
``incorrectly?
`
Thanks,
Scott Lamb
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**polyfit weirdness**,
*Scott Lamb* **<=**