Re: Correlation matrix is not positive definite

Posted by Art Kendall on Nov 29, 2011; 1:23pm
URL: http://spssx-discussion.165.s1.nabble.com/Correlation-matrix-is-not-positive-definite-tp4999980p5032362.html

We are closing in on this.
Is this correct? You have 3 Independent variables:
A type of bacterium between cases 4 levels a nominal level variable
B growth time repeated within cases 7 levels a ??? level variable
C wavelength repeated within cases a ratio level variable at 171 equal intervals

and one dependent variable intensity a ratio level variable.
That is 4788 cells with 1 measurement of intensity in each.

Is factor B repeats of a single parameter? i.e., are the levels ordered? At equal intervals?  7 distinct settings of different parameters, i.e., a nominal level variable?

Does your discipline use Q Factor Analysis?

Art Kendall
Social Research Consultants



On 11/28/2011 8:39 PM, viswa21 wrote:

Hi Art,
            * I am trying to find sets of profiles that are maximally
similar with the set and maximally different between the sets.*

All the bacteria were excited at single wavelength i.e. 225nm. Because
visually we cant differentiate  the spectrum, so we are doing PCA to find
out clusters of different bacteria at different places on PC1 Vs PC2.

To be more precise, I took emission spectra for four different kinds of
bacteria.

For each bacteria i took 7 scans or repetitions with slight changes in their
spectrum by changing physical parameter such as growth time. so there were
7*4=28 spectra. Now i applied data reduction steps. After clicking OK in
factor analysis popup window. The correlation matrix shows it is not
positive definite.

One of my colleague who had some idea tells me that, i need to carry F-test
or power test to determine number of variables which represents spectrum
rather having less number of variables. so plz advise me if there are any
solutions like that exits??

Thanks

Regards
visu

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