Page 229 - Excel for Scientists and Engineers: Numerical Methods

206 EXCEL: NUMERICAL METHODS

Option Base 1
Option Explicit
,+++++++++++++++++++i+++++++++++++++++++++i+i++++++ii+++
Function GaussSeidel(coeff-matrix, const-vector, Optional init-values)
' Solving systems of linear equations by the GaussSeidel method.
' Coefficients matrix cannot have zero diagonal element.
Dim Resultvector() As Double
Dim I As Integer, J As Integer, K As Integer
Dim N As Integer, Nlterations As Integer
Dim R As Integer, C As Integer
Dim ConvergeFlag As Boolean
Dim result As Double, sum As Double
N = coeff_matrix.Rows.Count
If coeff-matrix.Columns.Count <> N Or const-vector.Rows.Count -
c> N Then GaussSeidel = CVErr(x1ErrRef): Exit Function
ReDirn ResultVector(N)
' Following shows code for either fixed or adjustable iteration parameters.
' MaxChange and Maxlterations are set in the Tools/Options/Calculation menu.
tolerance = 0.00000001
Nlterations = 100
' User can specify optional initial values for the calculation
' This may be helpful for large arrays.
If Not (IsMissing(init-values)) Then
' Test if init-values is a Range.
If Not (IsError(init-values.Address)) Then
If init-values.Rows.Count = 1 Then
K = init-values.Columns.Count
Else
K = init-values.Rows.Count
End If
Else
' init-values must be an expression.
K = UBound(init-values)
End If
For I = 1 To K
ResultVector(1) = init-values(1)
Next I
End If
' Begin the iteration process.
For J = 1 To Nlterations
' Flag will be set to false if any of the result values has not yet converged.
ConvergeFlag = True
' Do each row in the matrix.
For R = 1 To N
sum = 0
' Sum each term in the row, but skip term on the diagonal.
ForC= 1 TON
sum = sum + coeff-matrix(R, C) * ResultVector(C) I