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NAME SPTTRF - compute the factorization of a real symmetric posi- tive definite tridiagonal matrix A SYNOPSIS SUBROUTINE SPTTRF( N, D, E, INFO ) INTEGER INFO, N REAL D( * ), E( * ) PURPOSE SPTTRF computes the factorization of a real symmetric posi- tive definite tridiagonal matrix A. If the subdiagonal elements of A are supplied in the array E, the factorization has the form A = L*D*L**T, where D is diagonal and L is unit lower bidiagonal; if the superdiago- nal elements of A are supplied, it has the form A = U**T*D*U, where U is unit upper bidiagonal. (The two forms are equivalent if A is real.) ARGUMENTS N (input) INTEGER The order of the matrix A. N >= 0. D (input/output) REAL array, dimension (N) On entry, the n diagonal elements of the tridiagonal matrix A. On exit, the n diagonal elements of the diagonal matrix D from the L*D*L**T factorization of A. E (input/output) REAL array, dimension (N-1) On entry, the (n-1) off-diagonal elements of the tridiagonal matrix A. On exit, the (n-1) off- diagonal elements of the unit bidiagonal factor L or U from the factorization of A. INFO (output) INTEGER = 0: successful exit < 0: if INFO = -i, the i-th argument had an illegal value > 0: if INFO = i, the leading minor of order i is not positive definite; if i < N, the factorization could not be completed, while if i = N, the factori- zation was completed, but D(N) = 0.