--- /dev/null
+#include "clapack.h"
+
+/* Table of constant values */
+
+static integer c__1 = 1;
+
+doublereal dlanst_(char *norm, integer *n, doublereal *d__, doublereal *e)
+{
+ /* System generated locals */
+ integer i__1;
+ doublereal ret_val, d__1, d__2, d__3, d__4, d__5;
+
+ /* Builtin functions */
+ double sqrt(doublereal);
+
+ /* Local variables */
+ integer i__;
+ doublereal sum, scale;
+ extern logical lsame_(char *, char *);
+ doublereal anorm;
+ extern /* Subroutine */ int dlassq_(integer *, doublereal *, integer *,
+ doublereal *, doublereal *);
+
+
+/* -- LAPACK auxiliary routine (version 3.1) -- */
+/* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. */
+/* November 2006 */
+
+/* .. Scalar Arguments .. */
+/* .. */
+/* .. Array Arguments .. */
+/* .. */
+
+/* Purpose */
+/* ======= */
+
+/* DLANST 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 symmetric tridiagonal matrix A. */
+
+/* Description */
+/* =========== */
+
+/* DLANST returns the value */
+
+/* DLANST = ( 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 DLANST as described */
+/* above. */
+
+/* N (input) INTEGER */
+/* The order of the matrix A. N >= 0. When N = 0, DLANST is */
+/* set to zero. */
+
+/* D (input) DOUBLE PRECISION array, dimension (N) */
+/* The diagonal elements of A. */
+
+/* E (input) DOUBLE PRECISION array, dimension (N-1) */
+/* The (n-1) sub-diagonal or super-diagonal elements of A. */
+
+/* ===================================================================== */
+
+/* .. Parameters .. */
+/* .. */
+/* .. Local Scalars .. */
+/* .. */
+/* .. External Functions .. */
+/* .. */
+/* .. External Subroutines .. */
+/* .. */
+/* .. Intrinsic Functions .. */
+/* .. */
+/* .. Executable Statements .. */
+
+ /* Parameter adjustments */
+ --e;
+ --d__;
+
+ /* Function Body */
+ if (*n <= 0) {
+ anorm = 0.;
+ } else if (lsame_(norm, "M")) {
+
+/* Find max(abs(A(i,j))). */
+
+ anorm = (d__1 = d__[*n], abs(d__1));
+ i__1 = *n - 1;
+ for (i__ = 1; i__ <= i__1; ++i__) {
+/* Computing MAX */
+ d__2 = anorm, d__3 = (d__1 = d__[i__], abs(d__1));
+ anorm = max(d__2,d__3);
+/* Computing MAX */
+ d__2 = anorm, d__3 = (d__1 = e[i__], abs(d__1));
+ anorm = max(d__2,d__3);
+/* L10: */
+ }
+ } else if (lsame_(norm, "O") || *(unsigned char *)
+ norm == '1' || lsame_(norm, "I")) {
+
+/* Find norm1(A). */
+
+ if (*n == 1) {
+ anorm = abs(d__[1]);
+ } else {
+/* Computing MAX */
+ d__3 = abs(d__[1]) + abs(e[1]), d__4 = (d__1 = e[*n - 1], abs(
+ d__1)) + (d__2 = d__[*n], abs(d__2));
+ anorm = max(d__3,d__4);
+ i__1 = *n - 1;
+ for (i__ = 2; i__ <= i__1; ++i__) {
+/* Computing MAX */
+ d__4 = anorm, d__5 = (d__1 = d__[i__], abs(d__1)) + (d__2 = e[
+ i__], abs(d__2)) + (d__3 = e[i__ - 1], abs(d__3));
+ anorm = max(d__4,d__5);
+/* L20: */
+ }
+ }
+ } else if (lsame_(norm, "F") || lsame_(norm, "E")) {
+
+/* Find normF(A). */
+
+ scale = 0.;
+ sum = 1.;
+ if (*n > 1) {
+ i__1 = *n - 1;
+ dlassq_(&i__1, &e[1], &c__1, &scale, &sum);
+ sum *= 2;
+ }
+ dlassq_(n, &d__[1], &c__1, &scale, &sum);
+ anorm = scale * sqrt(sum);
+ }
+
+ ret_val = anorm;
+ return ret_val;
+
+/* End of DLANST */
+
+} /* dlanst_ */