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

6       DTRTRS - a triangular system of the form   A * X = B or A**T * X = B,
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SYNOPSIS

9       SUBROUTINE DTRTRS( UPLO, TRANS, DIAG, N, NRHS, A, LDA, B, LDB, INFO )
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11           CHARACTER      DIAG, TRANS, UPLO
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13           INTEGER        INFO, LDA, LDB, N, NRHS
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15           DOUBLE         PRECISION A( LDA, * ), B( LDB, * )
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PURPOSE

18       DTRTRS solves a triangular system of the form
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20       where  A  is  a  triangular  matrix  of  order N, and B is an N-by-NRHS
21       matrix.  A check is made to verify that A is nonsingular.
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ARGUMENTS

25       UPLO    (input) CHARACTER*1
26               = 'U':  A is upper triangular;
27               = 'L':  A is lower triangular.
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29       TRANS   (input) CHARACTER*1
30               Specifies the form of the system of equations:
31               = 'N':  A * X = B  (No transpose)
32               = 'T':  A**T * X = B  (Transpose)
33               = 'C':  A**H * X = B  (Conjugate transpose = Transpose)
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35       DIAG    (input) CHARACTER*1
36               = 'N':  A is non-unit triangular;
37               = 'U':  A is unit triangular.
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39       N       (input) INTEGER
40               The order of the matrix A.  N >= 0.
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42       NRHS    (input) INTEGER
43               The number of right hand sides, i.e., the number of columns  of
44               the matrix B.  NRHS >= 0.
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46       A       (input) DOUBLE PRECISION array, dimension (LDA,N)
47               The  triangular  matrix  A.   If UPLO = 'U', the leading N-by-N
48               upper triangular part of the array A contains the upper  trian‐
49               gular  matrix,  and  the strictly lower triangular part of A is
50               not referenced.  If UPLO = 'L', the leading N-by-N lower trian‐
51               gular part of the array A contains the lower triangular matrix,
52               and the strictly upper triangular part of A is not  referenced.
53               If  DIAG  = 'U', the diagonal elements of A are also not refer‐
54               enced and are assumed to be 1.
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56       LDA     (input) INTEGER
57               The leading dimension of the array A.  LDA >= max(1,N).
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59       B       (input/output) DOUBLE PRECISION array, dimension (LDB,NRHS)
60               On entry, the right hand side matrix B.  On exit, if INFO =  0,
61               the solution matrix X.
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63       LDB     (input) INTEGER
64               The leading dimension of the array B.  LDB >= max(1,N).
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66       INFO    (output) INTEGER
67               = 0:  successful exit
68               < 0: if INFO = -i, the i-th argument had an illegal value
69               > 0: if INFO = i, the i-th diagonal element of A is zero, indi‐
70               cating that the matrix is singular and the solutions X have not
71               been computed.
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75 LAPACK routine (version 3.1)    November 2006                       DTRTRS(1)
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