The LA_TRISOL function is used in conjunction with the LA_TRIDC procedure to solve a set of n linear equations in n unknowns, AX = B, where A is a tridiagonal array. The parameter A is input not as the original array, but as its LU decomposition, created by the routine LA_TRIDC.
The LA_TRISOL function may also be used to solve for multiple systems of linear equations, with each column of B representing a different set of equations. In this case, the result is a k-by-n array where each of the k columns represents the solution vector for that set of equations.
LA_TRISOL is based on the following LAPACK routines:
|
Output Type |
LAPACK Routine |
|
Float |
sgttrs |
| Double |
dgttrs |
| Complex |
cgttrs |
|
Double complex |
zgttrs |
Examples
For an example of using this routine see LA_TRIMPROVE.
Syntax
Result = LA_TRISOL( AL, A, AU, U2, Index, B [, /DOUBLE] )
Return Value
The result is an n-element vector or k-by-n array.
Arguments
AL
The (n - 1) elements of the lower bidiagonal array, created by the LA_TRIDC procedure.
A
The n diagonal elements of the upper triangular array, created by the LA_TRIDC procedure.
AU
The (n - 1) superdiagonal elements of the upper triangular array, created by the LA_TRIDC procedure.
U2
The (n - 2) elements of the second superdiagonal of the upper triangular array, created by the LA_TRIDC procedure.
Index
An input vector, created by the LA_TRIDC procedure, containing the row permutations which occurred as a result of partial pivoting.
B
An n-element input vector containing the right-hand side of the linear system, or a k-by-n array, where each of the k columns represents a different linear system.
Keywords
DOUBLE
Set this keyword to use double-precision for computations and to return a double-precision (real or complex) result. Set DOUBLE = 0 to use single-precision for computations and to return a single-precision (real or complex) result. The default is /DOUBLE if AL is double precision, otherwise the default is DOUBLE = 0.
Version History
| 5.6 |
Introduced |
Resources and References
For details see Anderson et al., LAPACK Users' Guide, 3rd ed., SIAM, 1999.
See Also
LA_TRIDC, LA_TRIMPROVE, TRISOL
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