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# st: Problems with matrix multiplication and syminv

 From "G. Anderson" To statalist@hsphsun2.harvard.edu Subject st: Problems with matrix multiplication and syminv Date 14 Jun 2013 00:51:35 +0100

```Hi,

```
I am having problems with matrix multiplication and inverting matrices using Stata.
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I want to compute the inverse of the outer product of a matrix of variables, X Note that a lot of the values of X are zero-not sure if this is problematic)
```
so

matrix outerproduct=X'X
matrix invouterproduct=syminv(outerproduct)

```
The problem is when I calculate the syminv, I always get a row of zeros. It seems when I change the data, the location of this row of zeros changes.
```

```
A quick check of the rank of X using mata shows it is of full rank (47), but the rank of outerproduct is only 46- I'm not sure why i get this result but suspect it has something to do with the fact that I get a row of zeros.
```
Any ideas?

Thanks,

Gareth

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