###
Calling Sequence

Result = TRISOL(*
A, B, C, R*
)

###
Arguments

####
A

A vector of length *
n*
containing the *
n*
-1 sub-diagonal elements of A^{
T}
. The first element of *
A*
, A_{
0}
, is ignored.

####
B

An *
n*
-element vector containing the main diagonal elements of A^{
T}
.

####
C

An *
n*
-element vector containing the *
n*
-1 super-diagonal elements of A^{
T}
. The last element of *
C*
, *
C*
_{
n-1}
, is ignored.

####
R

An *
n*
-element vector containing the right hand side of the linear system

A^{
T}
U = R.

###
Example

To solve a tridiagonal linear system, begin with an array representing a real tridiagonal linear system. (Note that only three vectors need be specified; there is no need to enter the entire array shown.)

Define a vector A containing the sub-diagonal elements with a leading 0.0 element:

A = [0.0, 2.0, 2.0, 2.0]

Define B containing the main diagonal elements:

B = [-4.0, -4.0, -4.0, -4.0]

Define C containing the super-diagonal elements with a trailing 0.0 element:

C = [1.0, 1.0, 1.0, 0.0]

Define the right-hand side vector:

R = [6.0, -8.0, -5.0, 8.0]

Compute the solution and print:

result = TRISOL(A, B, C, R)

PRINT, result

IDL prints:

-1.00000 2.00000 2.00000 -1.00000

The exact solution vector is [-1.0, 2.0, 2.0, -1.0].