STBSV/DTBSV/CTBSV/ZTBSV

 

Solve triangular band system

 

ab

Array containing the n-by-ntriangular band matrix A

 

 

in the compressed form described above. The columns

 

 

of the band of A are stored in the columns of ab, and

 

 

the diagonals of the band of A are stored in the rows of

 

 

ab.

 

 

ldab

The leading dimension of array ab as declared in the

 

 

calling program unit, with ldab ≥ kd+1.

 

x

Array of length lenx = (n−1)⋅incx+1 containing the

 

 

right-hand-side n-vector x.

 

incx

Increment for the array x, incx ≠ 0:

 

 

incx > 0

x is stored forward in array x; that is,

 

 

 

xi is stored in x((i−1)⋅incx+1).

 

 

incx < 0

x is stored backward in array x; that

 

 

 

is, xi is stored in x((i−n)⋅incx+1).

 

 

Use incx = 1 if the vector x is stored contiguously in

 

 

array x, that is, if xi is stored in x(i). Refer to “BLAS

 

 

Indexing Conventions” in the introduction to

 

 

Chapter 2.

 

Output

x

The solution vector of the triangular band system

 

 

replaces the input.

Notes

These subprograms conform to specifications of the Level 2 BLAS.

 

The subprograms do not check for singularity of matrix A. A is singular if diag

 

= ’N’ or ’n’ and some aii

= 0. This condition causes a division by zero to occur.

Therefore, the program must detect singularity and take appropriate action to avoid a problem before calling any of these subprograms.

If an error in the arguments is detected, the subprograms call error handler XERBLA, which writes an error message onto the standard error file and terminates execution. The standard version of XERBLA (refer to the end of this chapter) can be replaced with a user-supplied version to change the error procedure.

306HP MLIB User’s Guide