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st: RE: RE: How can I get square roots of elements in a matrix,in Stata8.2?
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From |
"Nick Cox" <[email protected]> |
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To |
<[email protected]> |
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Subject |
st: RE: RE: How can I get square roots of elements in a matrix,in Stata8.2? |
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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
[email protected]
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
> [email protected]
>
> 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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