#include "blaswrap.h" #include "f2c.h" doublereal zlangt_(char *norm, integer *n, doublecomplex *dl, doublecomplex * d__, doublecomplex *du) { /* -- LAPACK auxiliary routine (version 3.1) -- Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. November 2006 Purpose ======= ZLANGT returns the value of the one norm, or the Frobenius norm, or the infinity norm, or the element of largest absolute value of a complex tridiagonal matrix A. Description =========== ZLANGT returns the value ZLANGT = ( 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 ZLANGT as described above. N (input) INTEGER The order of the matrix A. N >= 0. When N = 0, ZLANGT is set to zero. DL (input) COMPLEX*16 array, dimension (N-1) The (n-1) sub-diagonal elements of A. D (input) COMPLEX*16 array, dimension (N) The diagonal elements of A. DU (input) COMPLEX*16 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; doublereal ret_val, d__1, d__2; /* Builtin functions */ double z_abs(doublecomplex *), sqrt(doublereal); /* Local variables */ static integer i__; static doublereal sum, scale; extern logical lsame_(char *, char *); static doublereal anorm; extern /* Subroutine */ int zlassq_(integer *, doublecomplex *, integer *, doublereal *, doublereal *); --du; --d__; --dl; /* Function Body */ if (*n <= 0) { anorm = 0.; } else if (lsame_(norm, "M")) { /* Find max(abs(A(i,j))). */ anorm = z_abs(&d__[*n]); i__1 = *n - 1; for (i__ = 1; i__ <= i__1; ++i__) { /* Computing MAX */ d__1 = anorm, d__2 = z_abs(&dl[i__]); anorm = max(d__1,d__2); /* Computing MAX */ d__1 = anorm, d__2 = z_abs(&d__[i__]); anorm = max(d__1,d__2); /* Computing MAX */ d__1 = anorm, d__2 = z_abs(&du[i__]); anorm = max(d__1,d__2); /* L10: */ } } else if (lsame_(norm, "O") || *(unsigned char *) norm == '1') { /* Find norm1(A). */ if (*n == 1) { anorm = z_abs(&d__[1]); } else { /* Computing MAX */ d__1 = z_abs(&d__[1]) + z_abs(&dl[1]), d__2 = z_abs(&d__[*n]) + z_abs(&du[*n - 1]); anorm = max(d__1,d__2); i__1 = *n - 1; for (i__ = 2; i__ <= i__1; ++i__) { /* Computing MAX */ d__1 = anorm, d__2 = z_abs(&d__[i__]) + z_abs(&dl[i__]) + z_abs(&du[i__ - 1]); anorm = max(d__1,d__2); /* L20: */ } } } else if (lsame_(norm, "I")) { /* Find normI(A). */ if (*n == 1) { anorm = z_abs(&d__[1]); } else { /* Computing MAX */ d__1 = z_abs(&d__[1]) + z_abs(&du[1]), d__2 = z_abs(&d__[*n]) + z_abs(&dl[*n - 1]); anorm = max(d__1,d__2); i__1 = *n - 1; for (i__ = 2; i__ <= i__1; ++i__) { /* Computing MAX */ d__1 = anorm, d__2 = z_abs(&d__[i__]) + z_abs(&du[i__]) + z_abs(&dl[i__ - 1]); anorm = max(d__1,d__2); /* L30: */ } } } else if (lsame_(norm, "F") || lsame_(norm, "E")) { /* Find normF(A). */ scale = 0.; sum = 1.; zlassq_(n, &d__[1], &c__1, &scale, &sum); if (*n > 1) { i__1 = *n - 1; zlassq_(&i__1, &dl[1], &c__1, &scale, &sum); i__1 = *n - 1; zlassq_(&i__1, &du[1], &c__1, &scale, &sum); } anorm = scale * sqrt(sum); } ret_val = anorm; return ret_val; /* End of ZLANGT */ } /* zlangt_ */