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# Re: st: Problem computing eigenvalues, STATA vs. MATA

 From Steven Samuels <[email protected]> To [email protected] Subject Re: st: Problem computing eigenvalues, STATA vs. MATA Date Sun, 9 Jan 2011 12:57:17 -0500

Please note also: Statalist FAQ 8.2 "What is the correct way to write ‘Stata’?" "Stata is an invented word, not an acronym, and should not appear with all letters capitalized: please write “Stata”, not “STATA”. Mata is also an invented word, not an acronym."
```

Steve
[email protected]

On Jan 9, 2011, at 10:42 AM, Austin Nichols wrote:

Zachary Neal <[email protected]>:
You are confusing vectors and values there, and not sorting by values
after computing the eigensystem, but note that the only real
difference is that a couple of vectors are negated (any scalar
multiple of an eigenvector is also an eigenvector and the negation has
the same length so they are essentially equivalent) and Mata is using
quad precision to do the computations.

```
matrix define A = 0,1,1,0,0 \ 1,0,0,1,0 \ 1,0,0,0,1 \ 0,1,0,0,0 \ 0,0,1,0,0
```matrix symeigen vectors1 values1 = A
matrix list values1
matrix list vectors1
mata
values2 = 0
vectors2 = 0
symeigensystem(st_matrix("A"),vectors2,values2)
v2=sort((values2\vectors2)',1)'
v2[1,.]
v2[2..6,.]
end

On Sun, Jan 9, 2011 at 8:08 AM, Zachary Neal <[email protected]> wrote:
```
```I am trying to obtain the eigenvalues of a symmetric matrix.  However,
I get different results depending on whether I use STATA or MATA.  For
example:

```
matrix define A = 0,1,1,0,0 \ 1,0,0,1,0 \ 1,0,0,0,1 \ 0,1,0,0,0 \ 0,0,1,0,0
```matrix symeigen eigenvalues1 eigenvectors1 = A
matrix list eigenvalues1

mata: A = 0,1,1,0,0 \ 1,0,0,1,0 \ 1,0,0,0,1 \ 0,1,0,0,0 \ 0,0,1,0,0
mata: eigenvalues2 = 0
mata: eigenvectors2 = 0
mata: symeigensystem(A,eigenvalues2,eigenvectors2)
mata: eigenvalues2

In this case, eigenvalues1 does not equal eigenvalues2.  I believe the
results yielded by STATA (i.e. eigenvalues1) are what I'm looking for.

Why do these two sets of commands yield different results?  What
commands are necessary in MATA to yield the same eigenvalues that are
given by STATA?

Thank you
Zachary Neal
```
```
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