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From |
rraciborski@stata.com |

To |
statalist@hsphsun2.harvard.edu |

Subject |
st: spmat: banded matrix from inverse distances |

Date |
Tue, 05 Jul 2011 07:46:05 -0500 |

Laszlo Sandor <sandorl@gmail.com> has some questions about the user-written -spmat- command: > I have no fewer than 401,639 observations... even if I need to keep a band of > 500, say, I would still keep the size of the banded matrix below 400 MB... > Using an implementation of a useful sorting from graph theory, I think I could > code up populating a matrix of the inverse distances outside of Stata. Mata matrices are stored in double precision, thus with a band of 500 Laszlo would need 1.5Gb of storage space . di (401639*500*8) / 2^30 1.4962219 Given the size of Laszlo's dataset I doubt the Cuthill-McKee algorithm Laszlo referred to will reduce the bandwidth to something with which Laszlo can work. Laszlo also asks whether it is possible to use -spmat import- with a spatial-weighting matrix in a neighbor list format that contains distance information. This can be done by creating a text file in a GeoDa format as follows ============= begin example.gwt ============= 10 1 2 32.8 1 5 15.9 2 4 19.6 3 8 16.5 4 5 18.3 4 6 79.6 5 3 19.4 5 1 11.2 6 4 79.7 6 8 18.3 6 10 19.2 7 4 61.5 7 9 23.7 8 1 3.1 8 2 5.2 9 4 11.6 10 5 10.7 10 7 22.1 ============= end example.gwt ============= where '10' in the first line means there are a total of 10 spatial units and the remaining lines list unit i, unit j, and the distance between them. To import this information into an spmat object, Laszlo would code . spmat import obj using example.gwt, geoda At the moment, -spmat import- does not support importing .gwt files in a banded format. --Rafal rraciborski@stata.com * * 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/

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