[SciPy-user] eigenvector values (negative where it should be positive)

Carlos "Guâno" Grohmann carlos.grohmann@gmail....
Sun May 24 21:07:55 CDT 2009


Hello all

I'm working on some structural geology data, using numpy (I'm
following some class notes, so I can check my results). I have a set
of directional data (azimuth/dip):

12 42
18 40
22 48
15 30
10 42
20 30

First I read the data and create a matrix with the direction cosines like this:

#direction cosines relative to axis oriented north, east and down
# phi = longitude = azimuth (dip direction)
# theta = latitude = dip
# xi = cos(theta[i])*cos(phi[i])
# yi = cos(theta[i])*sin(phi[i])
# zi = sin(theta[i])
# Tmat = orientation matrix T
# Tmat = sum(xi2)    sum(xi.yi)    sum(xi.zi)
#        sum(yi.xi)  sum(yi2)      sum(yi.zi)
#        sum(zi.xi)  sum(zi.yi)    sum(zi2)

This is the matrix:

[[ 3.34172131  0.96327612  2.73061427]
 [ 0.96327612  0.29736701  0.78834422]
 [ 2.73061427  0.78834422  2.36091168]]


So far so good, but according to my example, the eigenvectors should look like:

  Vector 1 Vector 2 Vector 3
X  0.749    -0.590   -0.300
Y  0.217    -0.210    0.953
Z  0.626    0.779     0.029

and I have this:

[[-0.74913585 -0.59037777  0.30041565]
 [-0.21679731 -0.21002264 -0.95335692]
 [-0.62593482  0.77932315 -0.02934318]]


So, the values are OK, but the negative signs I don't understand.

any ideas are welcome

TIA

Carlos

-- 
Carlos Henrique Grohmann - Geologist D.Sc.
a.k.a. Guano - Linux User #89721
ResearcherID: A-9030-2008
carlos dot grohmann at gmail dot com
http://www.igc.usp.br/pessoais/guano/
_________________
"Good morning, doctors. I have taken the liberty of removing Windows
95 from my hard drive."
--The winning entry in a "What were HAL's first words" contest judged
by 2001: A SPACE ODYSSEY creator Arthur C. Clarke

Can’t stop the signal.


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