1STPTRI(1)                LAPACK routine (version 3.1)                STPTRI(1)
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NAME

6       STPTRI  -  the  inverse  of  a  real upper or lower triangular matrix A
7       stored in packed format
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SYNOPSIS

10       SUBROUTINE STPTRI( UPLO, DIAG, N, AP, INFO )
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12           CHARACTER      DIAG, UPLO
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14           INTEGER        INFO, N
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16           REAL           AP( * )
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PURPOSE

19       STPTRI computes the inverse of a real upper or lower triangular  matrix
20       A stored in packed format.
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ARGUMENTS

24       UPLO    (input) CHARACTER*1
25               = 'U':  A is upper triangular;
26               = 'L':  A is lower triangular.
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28       DIAG    (input) CHARACTER*1
29               = 'N':  A is non-unit triangular;
30               = 'U':  A is unit triangular.
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32       N       (input) INTEGER
33               The order of the matrix A.  N >= 0.
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35       AP      (input/output) REAL array, dimension (N*(N+1)/2)
36               On entry, the upper or lower triangular matrix A, stored colum‐
37               nwise in a linear array.  The j-th column of A is stored in the
38               array  AP as follows: if UPLO = 'U', AP(i + (j-1)*j/2) = A(i,j)
39               for 1<=i<=j; if UPLO = 'L', AP(i + (j-1)*((2*n-j)/2)  =  A(i,j)
40               for  j<=i<=n.   See  below  for  further details.  On exit, the
41               (triangular) inverse of the original matrix, in the same packed
42               storage format.
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44       INFO    (output) INTEGER
45               = 0:  successful exit
46               < 0:  if INFO = -i, the i-th argument had an illegal value
47               >  0:   if  INFO  =  i, A(i,i) is exactly zero.  The triangular
48               matrix is singular and its inverse can not be computed.
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FURTHER DETAILS

51       A triangular matrix A can be transferred to packed storage using one of
52       the following program segments:
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54       UPLO = 'U':                      UPLO = 'L':
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56             JC = 1                           JC = 1
57             DO 2 J = 1, N                    DO 2 J = 1, N
58                DO 1 I = 1, J                    DO 1 I = J, N
59                   AP(JC+I-1) = A(I,J)              AP(JC+I-J) = A(I,J)
60           1    CONTINUE                    1    CONTINUE
61                JC = JC + J                      JC = JC + N - J + 1
62           2 CONTINUE                       2 CONTINUE
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67 LAPACK routine (version 3.1)    November 2006                       STPTRI(1)
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