NAG FL Interface
f06wbf (dtfsm)

1 Purpose

2 Specification

3 Description

4 References

5 Arguments

1: $\mathbf{transr}$ – Character(1) Input

On entry: specifies whether the RFP representation of $A$ is normal or transposed.

$\mathbf{transr}=\text{'N'}$

The matrix $A$ is stored in normal RFP format.

$\mathbf{transr}=\text{'T'}$

The matrix $A$ is stored in transposed RFP format.

Constraint: $\mathbf{transr}=\text{'N'}$ or $\text{'T'}$.

2: $\mathbf{side}$ – Character(1) Input

On entry: specifies whether $B$ is operated on from the left or the right, or similarly whether $A$ (or its transpose) appears to the left or right of the solution matrix in the linear system to be solved.

$\mathbf{side}=\text{'L'}$

$B$ is pre-multiplied from the left. The system to be solved has the form $AX=\alpha B$ or $A^{\mathrm{T}}X=\alpha B$.

$\mathbf{side}=\text{'R'}$

$B$ is post-multiplied from the right. The system to be solved has the form $XA=\alpha B$ or $X{A}^{\mathrm{T}}=\alpha B$.

Constraint: $\mathbf{side}=\text{'L'}$ or $\text{'R'}$.

3: $\mathbf{uplo}$ – Character(1) Input

On entry: specifies whether $A$ is upper or lower triangular.

$\mathbf{uplo}=\text{'U'}$

$A$ is upper triangular.

$\mathbf{uplo}=\text{'L'}$

$A$ is lower triangular.

Constraint: $\mathbf{uplo}=\text{'U'}$ or $\text{'L'}$.

4: $\mathbf{trans}$ – Character(1) Input

On entry: specifies whether the operation involves $A^{-1}$ or $A^{-\mathrm{T}}$, i.e., whether or not $A$ is transposed in the linear system to be solved.

$\mathbf{trans}=\text{'N'}$

The operation involves $A^{-1}$, i.e., $A$ is not transposed.

$\mathbf{trans}=\text{'T'}$

The operation involves $A^{-\mathrm{T}}$, i.e., $A$ is transposed.

Constraint: $\mathbf{trans}=\text{'N'}$ or $\text{'T'}$.

5: $\mathbf{diag}$ – Character(1) Input

On entry: specifies whether $A$ has nonunit or unit diagonal elements.

$\mathbf{diag}=\text{'N'}$

The diagonal elements of $A$ are stored explicitly.

$\mathbf{diag}=\text{'U'}$

The diagonal elements of $A$ are assumed to be $1$, the corresponding elements of a are not referenced.

Constraint: $\mathbf{diag}=\text{'N'}$ or $\text{'U'}$.

6: $\mathbf{m}$ – Integer Input

On entry: $m$, the number of rows of the matrix $B$.

Constraint: $\mathbf{m}\ge 0$.

7: $\mathbf{n}$ – Integer Input

On entry: $n$, the number of columns of the matrix $B$.

Constraint: $\mathbf{n}\ge 0$.

8: $\mathbf{alpha}$ – Real (Kind=nag_wp) Input

On entry: the scalar $\alpha$.

9: $\mathbf{a}\left(*\right)$ – Real (Kind=nag_wp) array Input

Note: the dimension of the array a must be at least $\max (1,\mathbf{m}\times (\mathbf{m}+1)/2)$ if $\mathbf{side}=\text{'L'}$ and at least $\max (1,\mathbf{n}\times (\mathbf{n}+1)/2)$ if $\mathbf{side}=\text{'R'}$.

On entry: $A$, the $m\times m$ triangular matrix $A$ if $\mathbf{side}=\text{'L'}$ or the $n\times n$ triangular matrix $A$ if $\mathbf{side}=\text{'R'}$, stored in RFP format (as specified by transr). The storage format is described in detail in Section 3.3.3 in the F07 Chapter Introduction. If $\mathbf{alpha}=0.0$, a is not referenced.

10: $\mathbf{b}(\mathbf{ldb},*)$ – Real (Kind=nag_wp) array Input/Output

Note: the second dimension of the array b must be at least $\max (1,\mathbf{n})$.

On entry: the $m\times n$ matrix $B$.

If $\mathbf{alpha}=0$, b need not be set.

On exit: the updated matrix $B$, or similarly the solution matrix $X$.

11: $\mathbf{ldb}$ – Integer Input

On entry: the first dimension of the array b as declared in the (sub)program from which f06wbf is called.

Constraint: $\mathbf{ldb}\ge \max (1,\mathbf{m})$.

6 Error Indicators and Warnings

7 Accuracy

8 Parallelism and Performance

9 Further Comments

10 Example

10.1 Program Text

10.2 Program Data

10.3 Program Results