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st: RE: RE: How can I get square roots of elements in a matrix,in Stata8.2?


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: RE: How can I get square roots of elements in a matrix,in Stata8.2?
Date   Tue, 28 Aug 2007 13:41:24 +0100

I overlooked the question: Can I do it with Mata? 
The answer is yes. 

B = sqrt(A) 

is all there is to it. So you are missing out
and need to upgrade to 10, modulo availability of
funds. 

Nick 
n.j.cox@durham.ac.uk 

Nick Cox
 
> A -search- yields sources of advice: 
> 
> FAQ     . . . . . . . . . Performing element-by-element 
> operations on matrices
>         . . . . . . . . . . . . . . . . . . . . . . . . . . . 
> . .  A. McDowell
>         4/05    How do I perform element-by-element operations on
>                 matrices?
>                 http://www.stata.com/support/faqs/data/matrix.html
> 
> FAQ     . . . . . . . . . . .  How do I do elementwise 
> operations on a matrix?
>         . . . . . . . . . . . . . . . . . .  UCLA Academic 
> Technology Services
>         10/06   http://www.ats.ucla.edu/stat/stata/faq/elemmatrix.htm
> 
> but there is more to be said. 
> 
> The easiest solution in terms of your typing is to install 
> -matmap- from
> SSC. 
> 
> matmap A B, map(sqrt(@))
> 
> creates B which contains the roots of the elements of A. 
> 
> This is almost as easy and will develop understanding: 
> 
> mat B = A 
> forval i = 1/`= rowsof(A)' { 
> 	forval j = 1/`= colsof(A)' { 
> 		mat B[`i', `j'] = sqrt(A[`i, `j']) 
> 	}
> } 
> 
> The UCLA FAQ above does this kind of thing using -while-. That
> is here more cumbersome than using -forval-. 
> 
> Here is -matmap-. 
> 
> ---------------------------------------------------
> program define matmap 
> *! 1.0.0  NJC 23 August 2000
>         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
> --------------------------------------------------
> 
> Here is how, 7 years on, I would rewrite it for Stata 8.2 [sic]. 
> Not tested! 
> 
> 1. -forval- is nicer than -while-. 
> 2. Stata's matrices can now include missing values. 
> 3. Some other small changes.
> 
> So all the program does is set up two loops over
> the rows and columns and do your stuff elementwise. 
> 
> ----------------------------------------------- matmap8 
> *! 1.1.0  NJC 28 August 2007 
> program matmap8 
>         version 8.2
>         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 
>         }       
>         
>         local nr = rowsof(matrix(`A'))
>         local nc = colsof(matrix(`A'))
>         tempname C 
>         mat `C' = `A'  
> 
>         forval i = 1/`nr' {
>                 forval j = 1/`nc' {
>                         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
> ------------------------------------------------------
> 
> Nick 
> n.j.cox@durham.ac.uk 
> 
> Xiaoheng Zhang
>  
> > I am looking for a command or program to transfer a matrix 
> into a new
> > matrix with each element becoming its square root. How can I do this
> > in Stata 8.2?Can I do it in Stata 9.0 with mata?But 
> currently I do not
> > have Stata 9.0.Thank you.
> 

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