#include "blaswrap.h" #include "f2c.h" doublereal slangt_(char *norm, integer *n, real *dl, real *d__, real *du) { /* -- LAPACK auxiliary routine (version 3.1) -- Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. November 2006 Purpose ======= SLANGT returns the value of the one norm, or the Frobenius norm, or the infinity norm, or the element of largest absolute value of a real tridiagonal matrix A. Description =========== SLANGT returns the value SLANGT = ( max(abs(A(i,j))), NORM = 'M' or 'm' ( ( norm1(A), NORM = '1', 'O' or 'o' ( ( normI(A), NORM = 'I' or 'i' ( ( normF(A), NORM = 'F', 'f', 'E' or 'e' where norm1 denotes the one norm of a matrix (maximum column sum), normI denotes the infinity norm of a matrix (maximum row sum) and normF denotes the Frobenius norm of a matrix (square root of sum of squares). Note that max(abs(A(i,j))) is not a consistent matrix norm. Arguments ========= NORM (input) CHARACTER*1 Specifies the value to be returned in SLANGT as described above. N (input) INTEGER The order of the matrix A. N >= 0. When N = 0, SLANGT is set to zero. DL (input) REAL array, dimension (N-1) The (n-1) sub-diagonal elements of A. D (input) REAL array, dimension (N) The diagonal elements of A. DU (input) REAL array, dimension (N-1) The (n-1) super-diagonal elements of A. ===================================================================== Parameter adjustments */ /* Table of constant values */ static integer c__1 = 1; /* System generated locals */ integer i__1; real ret_val, r__1, r__2, r__3, r__4, r__5; /* Builtin functions */ double sqrt(doublereal); /* Local variables */ static integer i__; static real sum, scale; extern logical lsame_(char *, char *); static real anorm; extern /* Subroutine */ int slassq_(integer *, real *, integer *, real *, real *); --du; --d__; --dl; /* Function Body */ if (*n <= 0) { anorm = 0.f; } else if (lsame_(norm, "M")) { /* Find max(abs(A(i,j))). */ anorm = (r__1 = d__[*n], dabs(r__1)); i__1 = *n - 1; for (i__ = 1; i__ <= i__1; ++i__) { /* Computing MAX */ r__2 = anorm, r__3 = (r__1 = dl[i__], dabs(r__1)); anorm = dmax(r__2,r__3); /* Computing MAX */ r__2 = anorm, r__3 = (r__1 = d__[i__], dabs(r__1)); anorm = dmax(r__2,r__3); /* Computing MAX */ r__2 = anorm, r__3 = (r__1 = du[i__], dabs(r__1)); anorm = dmax(r__2,r__3); /* L10: */ } } else if (lsame_(norm, "O") || *(unsigned char *) norm == '1') { /* Find norm1(A). */ if (*n == 1) { anorm = dabs(d__[1]); } else { /* Computing MAX */ r__3 = dabs(d__[1]) + dabs(dl[1]), r__4 = (r__1 = d__[*n], dabs( r__1)) + (r__2 = du[*n - 1], dabs(r__2)); anorm = dmax(r__3,r__4); i__1 = *n - 1; for (i__ = 2; i__ <= i__1; ++i__) { /* Computing MAX */ r__4 = anorm, r__5 = (r__1 = d__[i__], dabs(r__1)) + (r__2 = dl[i__], dabs(r__2)) + (r__3 = du[i__ - 1], dabs(r__3) ); anorm = dmax(r__4,r__5); /* L20: */ } } } else if (lsame_(norm, "I")) { /* Find normI(A). */ if (*n == 1) { anorm = dabs(d__[1]); } else { /* Computing MAX */ r__3 = dabs(d__[1]) + dabs(du[1]), r__4 = (r__1 = d__[*n], dabs( r__1)) + (r__2 = dl[*n - 1], dabs(r__2)); anorm = dmax(r__3,r__4); i__1 = *n - 1; for (i__ = 2; i__ <= i__1; ++i__) { /* Computing MAX */ r__4 = anorm, r__5 = (r__1 = d__[i__], dabs(r__1)) + (r__2 = du[i__], dabs(r__2)) + (r__3 = dl[i__ - 1], dabs(r__3) ); anorm = dmax(r__4,r__5); /* L30: */ } } } else if (lsame_(norm, "F") || lsame_(norm, "E")) { /* Find normF(A). */ scale = 0.f; sum = 1.f; slassq_(n, &d__[1], &c__1, &scale, &sum); if (*n > 1) { i__1 = *n - 1; slassq_(&i__1, &dl[1], &c__1, &scale, &sum); i__1 = *n - 1; slassq_(&i__1, &du[1], &c__1, &scale, &sum); } anorm = scale * sqrt(sum); } ret_val = anorm; return ret_val; /* End of SLANGT */ } /* slangt_ */