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From |
Kit Baum <kitbaum@mac.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
st: re: interaction of column matrix |

Date |
Fri, 19 Oct 2007 06:58:26 -0400 |

Abdel wrote

I've written this mata function as a solution to my own question yesterday.

horizontal direct product (hdp).

--------begin code------------

version 9.2

local mydir "."

mata:

mata clear

real matrix hdp(real matrix A, real matrix B)

{

assert(rows(A)==rows(B))

real scalar n

real matrix C

n=rows(A)

C=J(n,1,.)

for (i=1; i<=cols(A); i++) {

C=C,(A[.,i]:*B)

}

C=C[.,2..cols(C)]

return(C)

}

I've never heard of a 'horizontal direct product' but in a 2x2 example it seems to be the first and last rows of a conventional Kronecker product:

: a

1 2

+---------+

1 | 1 2 |

2 | 3 4 |

+---------+

: b

1 2

+---------+

1 | 5 6 |

2 | 0 1 |

+---------+

: c

1 2 3 4

+---------------------+

1 | 5 6 10 12 |

2 | 0 3 0 4 |

+---------------------+

: a#b

1 2 3 4

+---------------------+

1 | 5 6 10 12 |

2 | 0 1 0 2 |

3 | 15 18 20 24 |

4 | 0 3 0 4 |

+---------------------+

For a 3x3 example, it is the 1st, 5th and 9th rows of the Kronecker product. Thus it appears that whatever this construction might be it could be generated from a Kronecker.

Kit Baum, Boston College Economics and DIW Berlin

http://ideas.repec.org/e/pba1.html

An Introduction to Modern Econometrics Using Stata:

http://www.stata-press.com/books/imeus.html

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**Follow-Ups**:**Re: st: re: interaction of column matrix***From:*"Abdel Rahmen El Lahga" <rahmen.lahga@gmail.com>

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