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NAG[f07bdc] NAG[nag_dgbtrf] - factorization of real by band matrix
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Calling Sequence
f07bdc(kl, ku, ab, ipiv, 'm'=m, 'n'=n, 'fail'=fail)
nag_dgbtrf(. . .)
Parameters
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kl - integer;
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On entry: , the number of subdiagonals within the band of the matrix .
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Constraint: . .
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ku - integer;
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On entry: , the number of superdiagonals within the band of the matrix .
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Constraint: . .
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ab - 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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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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'm'=m - integer; (optional)
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Default value: the first dimension of the array ab.
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On entry: , the number of rows of the matrix .
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Constraint: . .
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'n'=n - integer; (optional)
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Default value: the second dimension of the array ab.
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On entry: , the number of columns 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_dgbtrf (f07bdc) computes the factorization of a real by band matrix.
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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: .
On entry, . Constraint: .
On entry, . Constraint: .
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 factor is exactly singular.
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Further Comments
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The total number of floating-point operations varies between approximately and , depending on the interchanges, assuming and .
A call to nag_dgbtrf (f07bdc) may be followed by calls to the functions:
The complex analogue of this function is f07brc (nag_zgbtrf).
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Examples
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>
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m := 4:
n := 4:
kl := 1:
ku := 2:
ab := Matrix([[0, -0.23, 2.54, -3.66, 0], [-6.98, 2.46, -2.73, -2.13, 0], [2.56, 2.46, 4.07, 0, 0], [-4.78, -3.82, 0, 0, 0]], datatype=float[8], order='C_order'):
ipiv := Vector(4, datatype=integer[kernelopts('wordsize')/8]):
NAG:-f07bdc(kl, ku, ab, ipiv, 'm' = m, 'n' = n):
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