# Re: st: RE: Matrix manipulation of regression results

 From Herb Smith <[email protected]> To [email protected] Subject Re: st: RE: Matrix manipulation of regression results Date Fri, 5 Jan 2007 17:52:00 -0500 (EST)

```Wow -- and thanks!  This makes me like the two or three line Cholesky
work-around that much better, at least for a vector!

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On Fri, 5 Jan 2007, Nick Cox wrote:

> -matmap- from SSC offers users of Stata 6 .. 8
> a way to get element-wise square roots (and more
> besides).
>
> Here is the program, and pretty horrible it is
> too. I didn't do anything further with it because
> I became aware that Bill Gould had a much better program
> for elementwise stuff, but he never got round to
> releasing it, given the alternative he was developing
> called Mata.
>
> For Stata 8, -matmap- can be rewritten, as below.
>
> -------------------------- matmap from SSC
> *! 1.0.0  NJC 23 August 2000
> program define matmap
>         version 6.0
>         gettoken A 0 : 0
>         gettoken B 0 : 0, parse(" ,")
>         syntax , Map(str) [ Symbol(str) ]
>
>         if "`symbol'" == "" { local symbol "@" }
>
>         if !index("`map'","`symbol'") {
>                 di in r "map( ) does not contain `symbol'"
>                 exit 198
>         }
>
>         local nr = rowsof(matrix(`A'))
>         local nc = colsof(matrix(`A'))
>
>         tempname C val
>         mat `C' = `A'
>
>         local i 1
>         while `i' <= `nr' {
>                 local j 1
>                 while `j' <= `nc' {
>                         local exp : /*
>                         */ subinstr local map "`symbol'" "`A'[`i',`j']", all
>                         scalar `val' = `exp'
>                         if `val' == . {
>                                 di in r "matrix would have missing values"
>                                 exit 504
>                         }
>                         mat `C'[`i',`j'] = `val'
>                         local j = `j' + 1
>                 }
>                 local i = `i' + 1
>         }
>
>         mat `B' = `C' /* allows overwriting of either `A' or `B' */
> end
> ----------------------------------------
>
> --------------------------- matmap8
> *! 1.1.0  NJC 5 January 2007
> program matmap8
> 	version 8
> 	gettoken A 0 : 0
> 	gettoken B 0 : 0, parse(" ,")
> 	syntax , Map(str) [ Symbol(str) ]
>
> 	if "`symbol'" == "" local symbol "@"
>
> 	if !index("`map'","`symbol'") {
> 		di as err "map() does not contain `symbol'"
> 		exit 198
> 	}
>
> 	tempname C val
> 	mat `C' = `A'
>
> 	forval i = 1/`= rowsof(matrix(`A'))' {
>         	forval j = 1/`= colsof(matrix(`A'))' {
> 			local exp : ///
> 			subinstr local map "`symbol'" "`A'[`i',`j']", all
> 			mat `C'[`i',`j'] = `exp'
> 	        }
> 	}
>
> 	mat `B' = `C' /* allows overwriting of either `A' or `B' */
> end
> ---------------------------------
>
> But the best way to do e.w. square roots is like this:
>
> mat A = J(5,5,3)
> forval i = 1/5 {
> 	forval j = 1/5 {
> 		mat A[`i',`j'] = sqrt(A[`i',`j'])
> 	}
> }
>
> Nick
> [email protected]
>
> Herb Smith
> >
> > Mis-step 2:  Okay, what about using the old -matrix-
> > commands?  When I had
> > a vector of coefficient variances, I could locate within
> > -mata- a simple
> > command for taking element-by-element square roots, but not
> > under the old
> > -matrix- commands.  I ended up turning this vector into a
> > diagonal matrix
> > and getting square roots via Cholesky; but this is inelegant
> > and hardly
> > the sort of thing that gets social science graduate students
> > into using a
> > set of commands to do things....
>
> *
> *   For searches and help try:
> *   http://www.stata.com/support/faqs/res/findit.html
> *   http://www.stata.com/support/statalist/faq
> *   http://www.ats.ucla.edu/stat/stata/
>
*
*   For searches and help try:
*   http://www.stata.com/support/faqs/res/findit.html
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/
```