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Subject:

LINEAR ALGEBRA QUESTION

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Thu, 15 Jan 2004 02:07:22 -0800

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 ```***** To join INSNA, visit http://www.sfu.ca/~insna/ ***** I'm finishing up a matrix multiplication problem for an ASA paper and have run into a question that has stumped me. I have two bimodal binary matrices, one for 1980 and one for 1985. They are conformable, with actors on rows and practices on columns. I want to multiply the first (1980) by the transpose of the second (1985-T) to get a count of frequency overlap ("M") between the two years. This produces an asymmetric matrix ("M") because, while the number of actors are the same for both years, the number of ties vary. I want to multiply the new matrix ("M") by the inverse of the row sum of the earlier 1980 matrix to get a percentage of ties retained across years. Problem 1: The new product is also asymmetric and I am unable to determine how to read this with regards to time. That is, since the off diagonal cells are asymmetric, how do I determine if the flow from 1980 to 1985 is on the upper or lower diagonal? Problem 2: Should I multiply "M" by the *transpose* of the inverted row sum or just the inverted row sum? This is a simple question for a single year *symmetric* matrix, (which simply produces the transpose of the former). However these two vectors produce quite different results in the asymmetric multi-year matrix. Any help is appreciated. Best, Michael ________________________________________________________________ Michael Bourgeois Department of Sociology University of California Santa Barbara, CA 93106-9430 (805) 695-8786 We shall not cease from exploration And the end of all our exploring Will be to arrive where we started And know the place for the first time.       - T.S. Eliot, Little Gidding _________________________________________________ _____________________________________________________________________ SOCNET is a service of INSNA, the professional association for social network researchers (http://www.sfu.ca/~insna/). To unsubscribe, send an email message to [log in to unmask] containing the line UNSUBSCRIBE SOCNET in the body of the message.```