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Path: utzoo!watmath!clyde!burl!ulysses!gamma!epsilon!egs
From: egs@epsilon.UUCP (Ed Sheppard)
Newsgroups: net.math
Subject: Re: Determinant Evaluation
Message-ID: <36@epsilon.UUCP>
Date: Sun, 24-Feb-85 01:51:40 EST
Article-I.D.: epsilon.36
Posted: Sun Feb 24 01:51:40 1985
Date-Received: Wed, 27-Feb-85 03:53:50 EST
References: <3300010@uokvax.UUCP>
Organization: BELLCORE, Livingston, NJ
Lines: 31

> Give a method to find the determinant of a 1000 by 1000 matrix
> using recursion.

Forgive the Fortranishness of this.

float	determ(n,a)
int	n;
float	a[n][n];	/* ugh! */
{
	int	i, j;

	if(n==1 || a[0][0]==0)
	{
		return(a[0][0]);
	}
	for(i=1; i<n; ++i)
	{
		factor = a[i][0]/a[0][0];
		for(j=1; j<n; ++j)
		{
			a[i][j] -= factor*a[0][j];
		}
	}
	return(a[0][0]*determ(n-1,&a[1][1]));	/* ditto */
}

You'll note the recursion is totally unneeded. Are there any faster
methods that use recursion to better effect?

						Ed Sheppard
						Bellcore