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# spline cubic rutine with VB5

Posted on 2000-05-12
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I need a VB5.0 function able to do a smoth curve since a several datas from 2d array using spline cubic method
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Question by:rsilva
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Accepted Solution

bhess1 earned 5 total points
ID: 2806167
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LVL 28

Expert Comment

ID: 2806269
Hi
1. Do you need local (3 points) or global (all points) spline?
2. Do you need interpolation or extrapolation too?
3. I'm afraid you forgot to add some zeroes to points value <smile>
Cheers
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Author Comment

ID: 2806354
1. all points
2. interpolation
3. I lost my points because I put the
questions first in a wrong topic area
sorry, but I don't have more points
availables :(
0

LVL 28

Expert Comment

ID: 2806410
Hi
just one more question - plz, describe your 2d array - is this A(n,2) or A(2,n) dimension, is it zero or 1 bazed. Or you have 2 one-dim arrays?
for example:
A(0,0) = X(0)
A(0,1) = Y(0)
A(1,0) = X(1)
etc...
Cheers
0

LVL 28

Expert Comment

ID: 2806496
Ok, here it is.
I assume, you have 1 based 2dim array,like this:
A(1,1) = X(1)
A(1,2) = X(2)
A(1,3) = X(3)
A(2,1) = Y(1)
A(2,2) = Y(2)
A(2,3) = Y(3)
If not, I specially work with X() and Y() arrays so you can change code.
Place PictureBox, command button and TextBox (multiline) on form. Form code:

Option Explicit
Option Base 1
Dim M() As Single
Dim X() As Single, Y() As Single
Dim TempArr() As Single

Private Sub PrepareSpline(inpArr() As Single)
Dim n As Integer, i As Integer
Dim L() As Single, R() As Single, S() As Single
Dim D As Single, E As Single, F As Single, H As Single, P As Single
n = UBound(inpArr, 2)
If n < 2 Then Exit Sub
ReDim M(n), X(n), Y(n), L(n), R(n), S(n)
For i = 1 To n
X(i) = inpArr(1, i)
Y(i) = inpArr(2, i)
Next i
D = X(2) - X(1):  E = (Y(2) - Y(1)) / D
For i = 2 To n - 1
H = D: D = X(i + 1) - X(i)
If D = 0 Then D = 0.0001
F = E: E = (Y(i + 1) - Y(i)) / D
L(i) = D / (D + H)
R(i) = 1 - L(i)
S(i) = 6 * (E - F) / (D + H)
Next i
For i = 2 To n - 1
P = 1 / (R(i) * L(i - 1) + 2)
L(i) = -L(i) * P
S(i) = (S(i) - R(i) * S(i - 1)) * P
Next i
M(n) = 0: L(n - 1) = S(n - 1): M(n - 1) = L(n - 1)
For i = n - 2 To 1 Step -1
L(i) = L(i) * L(i + 1) + S(i)
M(i) = L(i)
Next i
End Sub

Private Function CalcValue(arg As Single) As Single
Dim ret As Single, i As Integer, n As Integer
Dim D As Single, H As Single, P As Single, R As Single
n = UBound(X)
For i = 1 To n
If arg < X(i) Then Exit For
Next i
Select Case i
Case 1    ' arg less then x(1) -> Extrapolation
D = X(2) - X(1)
If D = 0 Then D = 0.0001
ret = -D * M(2) / 6 + (Y(2) - Y(1)) / D
ret = ret * (arg - X(1)) + Y(1)
Case n + 1 ' arg greater then x(n) -> Extrapolation
D = X(n) - X(n - 1)
If D = 0 Then D = 0.0001
ret = D * M(n - 1) / 6 + (Y(n) - Y(n - 1)) / D
ret = ret * (arg - X(n)) + Y(n)
Case Else  'interpolation
D = X(i) - X(i - 1): H = arg - X(i - 1)
R = X(i) - arg: P = D * D / 6
ret = (M(i - 1) * R ^ 3 + M(i) * H ^ 3) / (6 * D)
ret = ret + ((Y(i - 1) - M(i - 1) * P) * R + (Y(i) - M(i) * P) * H) / D
End Select
CalcValue = ret
End Function

Private Sub Command1_Click()
PrepareSpline TempArr
DrawCurve 1
End Sub

Text1 = ""
Picture1.FillColor = vbRed
Picture1.FillStyle = vbSolid
End Sub

Private Sub Picture1_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single)
Dim i As Integer
Static n1 As Integer
If Button = 1 Then
n1 = n1 + 1
ReDim Preserve TempArr(2, n1)
TempArr(1, n1) = X
TempArr(2, n1) = Y
Text1 = Text1 & vbCrLf & TempArr(1, n1) & vbTab & TempArr(2, n1)
Picture1.Circle (X, Y), 50
End If
End Sub

Private Sub DrawCurve(iStep As Integer)
Dim i As Integer
Picture1.PSet (X(LBound(X)), CalcValue(X(LBound(X))))
For i = X(LBound(X)) + iStep To X(UBound(X)) Step iStep
Picture1.Line -(i, CalcValue(CSng(i)))
Next i
End Sub

' click on picturebox to draw points, then press command button
' sometimes you can received overflow or division by zero - it's depend on array value. You can fixed this yourself. (I've already spend 3 hours for coding and have no more time). Or I'll fix it after weekend.

Cheers

0

Author Comment

ID: 2814307
Thanks for help me, the rutines
works perfect..!!
regards,
Ricardo
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