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NAG[f07mjc] NAG[nag_dsytri] - Inverse of real symmetric indefinite matrix, matrix already factorized by f07mdc (nag_dsytrf)
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Calling Sequence
f07mjc(uplo, a, ipiv, 'n'=n, 'fail'=fail)
nag_dsytri(. . .)
Parameters
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uplo - String;
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On entry: indicates how has been factorized.
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Constraint: "Nag_Upper" or "Nag_Lower". .
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a - Matrix(1..dim1, 1..dim2, datatype=float[8], order=order);
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Note: this array may be supplied in Fortran_order or C_order , as specified by order. All array parameters must use a consistent order.
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If , the upper triangle of is stored in the upper triangular part of the array.
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If , the lower triangle of is stored in the lower triangular part of the array.
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ipiv - Vector(1..dim, datatype=integer[kernelopts('wordsize')/8]);
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Note: the dimension, dim, of the array ipiv must be at least .
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On entry: details of the interchanges and the block structure of , as returned by f07mdc (nag_dsytrf).
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'n'=n - integer; (optional)
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Default value: the dimension of the array a.
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On entry: , the order of the matrix .
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Constraint: . .
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'fail'=fail - table; (optional)
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The NAG error argument, see the documentation for NagError.
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Description
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Purpose
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nag_dsytri (f07mjc) computes the inverse of a real symmetric indefinite matrix , where has been factorized by f07mdc (nag_dsytrf).
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Error Indicators and Warnings
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"NE_ALLOC_FAIL"
Dynamic memory allocation failed.
"NE_BAD_PARAM"
On entry, argument had an illegal value.
"NE_INT"
On entry, . Constraint: .
"NE_INTERNAL_ERROR"
An internal error has occurred in this function. Check the function call and any array sizes. If the call is correct then please consult NAG for assistance.
"NE_SINGULAR"
The block diagonal matrix is exactly singular.
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Further Comments
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The total number of floating-point operations is approximately .
The complex analogues of this function are f07mwc (nag_zhetri) for Hermitian matrices and f07nwc (nag_zsytri) for symmetric matrices.
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Examples
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>
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uplo := "Nag_Lower":
n := 4:
a := Matrix([[1.335954681697555, 0, 0, 0], [-0.6975109160126703, -1.905898246668038, 0, 0], [0.8273386982024001, 0.7403045011146071, 3.494530386740331, 0], [0.6353591160220995, -0.3480662983425414, -1.138121546961326, -1.81]], datatype=float[8], order='C_order'):
ipiv := Vector([1, 2, 3, 4], datatype=integer[kernelopts('wordsize')/8]):
NAG:-f07mjc(uplo, a, ipiv, 'n' = n):
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