# Why Thomas Algorithm for tridiagonal systems?

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 June 29, 1999, 08:23 Why Thomas Algorithm for tridiagonal systems? #1 Yogesh Talekar Guest   Posts: n/a Why onlt Thomas' alorithm is used for solving tri-diagonal system and Why not GAUSS elimination which is much simpler? IS there anything in literature.

 June 29, 1999, 10:21 Re: Why Thomas Algorithm for tridiagonal systems? #2 Jim Park Guest   Posts: n/a Am I forgetting something (entirely possible!)? Isn't the Thomas algorithm just a degenerate Gauss elimination operating on a tridiagonal coefficient matrix?

 June 29, 1999, 10:52 Re: Why Thomas Algorithm for tridiagonal systems? #3 John C. Chien Guest   Posts: n/a (1). There are a couple of books you can read. (2). "Numerical Methods fo Engineering Application" by Joel H. Ferzier, published by John Wiley & Sons 1981. ISBN-0-471-06336-3 (3). "Applied Iterative Methods" by Louis A. Hageman & David M. Young, published by Academic Press 1981,ISBN 0-12-313340-8. (4). Thomas algorithm is used to solve the tri-diagonal system of equations as part of line implicit method. There are also many point iterative methods available. Sometimes, I just use point S.O.R. method for easy programming. It is faster to use line implicit method when the total number of mesh points becomes large. Try to read the Ferzier's book first. (There are also other books by David Young).

 June 29, 1999, 20:04 Re: Why Thomas Algorithm for tridiagonal systems? #4 Duane Baker Guest   Posts: n/a Correction: Ferziger NOT Ferzier! good book!

 June 30, 1999, 07:05 Re: Why Thomas Algorithm for tridiagonal systems? #5 John C. Chien Guest   Posts: n/a (1). You are right. But it looks smoother and easier to write this way. (2). We will have to convince the author to change the name. Or we will give the author another name called "fuzzy" , "fuzzy joe". (3). Don't try to read between the keyboard characters.

 June 30, 1999, 20:01 Re: Why Thomas Algorithm for tridiagonal systems? #6 T.J. Wanat Guest   Posts: n/a The Thomas alogorithm is a specialized form of Gauss elimination that is faster and more accurate (you reduce the total number of operations, thus reducing the truncation and round-off error that accumulates for large systems). I recommend using it whenever possible.

 July 15, 1999, 13:56 Re: Why Thomas Algorithm for tridiagonal systems? #7 Edward C. Chan Guest   Posts: n/a Thomas' Algorithm is a special case of Gaussian elimination where the incident matrix consists of only the diagonal, and its immediate east and west neighbours (when the problem is 1D.) As with Gaussian elimination, it is an exact solver and it takes very little time to implement and execute. If you need the code, I can give it to you (in C++) Cheers, Ed.

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