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From |
"Nick Cox" <n.j.cox@durham.ac.uk> |

To |
<statalist@hsphsun2.harvard.edu> |

Subject |
st: RE: element wise division of matrices |

Date |
Wed, 30 Jul 2008 21:30:09 +0100 |

Possibly more people know about Mata now than about Stata's old matrix language, so I'll point out that elementwise division of matrices is possible in Stata using -matewd- from STB-50: STB-50 dm69 . . . . . . . . . . . . . . . . . . Further new matrix commands (help matdelrc, matewm, matmad, matpow if installed) . . . N. J. Cox 7/99 pp.5--9; STB Reprints Vol 9, pp.29--34 collection of new matrix commands providing additional matrix checking, management, element-wise operators, maximum absolute difference, and power See also STB-39 dm49 . . . . . . . . . . . . . . . . . . . . Some new matrix commands (help matfunc, varfunc if installed) . . . . . . . . . . . J. Weesie 9/97 pp.17--20; STB Reprints Vol 7, pp.43--48 collection of new matrix commands; several for explicit matrices and a few for implicit matrices (i.e., variables) STB-56 dm79 . . . . . . . . . . . . . . . . . . Yet more new matrix commands (help matcorr, matewmf, matvsort, svmat2 if installed) . . N. J. Cox 7/00 pp.4--8; STB Reprints Vol 10, pp.17--23 commands to produce a correlation matrix, elementwise monadic function of another matrix, selected subsets of matrix rows and columns, vec or vech of a matrix, elements sorted within a vector, matrix from a vector, and commands to save matrices I've unlimited respect for Mata, but it is not obvious to me that it is a better language for quite what you are doing than Stata itself -- and I don't mean Stata's matrix language either. Presumably your rows and columns have identities that have meaning to you. Looking at 400 X 400 matrices of such a kind is not easy in Mata. If you represent your matrices by variables, Row identifier Col identifier Cell values for matrix 1 Cell values for matrix 2 ... Then elementwise division is naturally just division and most other basic analyses will be equally trivial. Nick n.j.cox@durham.ac.uk Victor, Jennifer Nicoll Thanks to Nick for recommending a running sum of matrices for my problem yesterday. I worked like a dream. Now I have a new problem. I have created two matrices in Stata using the matrix commands. One is called "rawsum," a 438x1010 matrix. The other is "bothvoting," also a 438x1010 matrix. I need to create matrix agreecount=(rawsum+bothvoting)/2. No problem. Now I need to create matrix agreerate=agreecount/bothvoting, where each i,j of 'agreecount' is divided by each i,j of 'bothvoting'. I cannot find a command in Stata's matrix commands to do this type of element-wise division. So, I've moved into Mata. Mata has a simple element-wise division command: X=A:/B. But, I am a novice Mata-user and I cannot figure out how to get my 438x438 matrix into Mata. So, I've converted it back to a dataset using the 'svmat' command and I'm trying to get the data into Mata using the 'st_view' command. My data has 438 observations and 438 variables. Essentially, I want to use the command: st_view(x., ., "agreecount1",..."agreecount438") ...then do the same with the 'bothvoting' data, then execute the e-w division command. I've tried using the 'for' command but cannot figure out the successful execution of a loop in Mata because the syntax is different than Stata's. How can I do this? Or can you provide a more elegant solution? * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**References**:**st: element wise division of matrices***From:*"Victor, Jennifer Nicoll" <jnvictor@pitt.edu>

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