PSI sics-cvs-psi_pre-ansto

matrix/matinv.c

@@ -0,0 +1,76 @@
+/*
+*-----------------------------------------------------------------------------
+*	file:	matinv.c
+*	desc:	matrix inversion
+*	by:	ko shu pui, patrick
+*	date:	24 nov 91 v0.1
+*	revi:	14 may 92 v0.2
+*	ref:
+*       [1] Mary L.Boas, "Mathematical Methods in the Physical Sciene,"
+*	John Wiley & Sons, 2nd Ed., 1983. Chap 3.
+*
+*	[2] Kendall E.Atkinson, "An Introduction to Numberical Analysis,"
+*	John Wiley & Sons, 1978.
+*
+*-----------------------------------------------------------------------------
+*/
+#include <stdio.h>
+#include <math.h>
+
+#ifdef	__TURBOC__
+#include <alloc.h>
+#else
+#include <malloc.h>
+#endif
+
+#include "matrix.h"
+
+
+/*
+*-----------------------------------------------------------------------------
+*	funct:	mat_inv
+*	desct:	find inverse of a matrix
+*	given:	a = square matrix a
+*	retrn:	square matrix Inverse(A)
+*		NULL = fails, singular matrix, or malloc() fails
+*-----------------------------------------------------------------------------
+*/
+MATRIX mat_inv( a )
+MATRIX a;
+{
+	MATRIX	A, B, C, P;
+	int	i, j, n;
+	double	temp;
+
+	n = MatCol(a);
+	A = mat_copy(a);
+	B = mat_creat( n, 1, UNDEFINED );
+	C = mat_creat( n, n, UNDEFINED );
+	P = mat_creat( n, 1, UNDEFINED );
+
+	/*
+	*	- LU-decomposition -
+	*	also check for singular matrix
+	*/
+	if (mat_lu(A, P) == -1)
+		{
+		mat_free(A);
+		mat_free(B);
+		mat_free(C);
+		mat_free(P);
+
+		return (NULL);
+		}
+
+	for (i=0; i<n; i++)
+		{
+		mat_fill(B, ZERO_MATRIX);
+		B[i][0] = 1.0;
+		mat_backsubs1( A, B, C, P, i );
+		}
+
+	mat_free(A);
+	mat_free(B);
+	mat_free(P);
+	return (C);
+}