I've been trying to do Modular exponentiation in VBA for use in MS excel, but there seems to be a logical error which crashes Excel everytime i try to use the formula.
Function expmod(ax As Integer, bx As Integer, cx As Integer)
' Declare a, b, and c
Dim a As Integer
Dim b As Integer
Dim c As Integer
' Declare new values
Dim a1 As Integer
Dim p As Integer
' Set variables
a = ax
b = bx
c = cx
a1 = a Mod c
p = 1
' Loop to use Modular exponentiation
While b > 0
a = ax
If (b Mod 2 <> 0) Then
p = p * a1
b = b / 2
End If
a1 = (a1 * a1) Mod c
Wend
expmod = a1
End Function
I used the pseudocode which was provided here.
Here is an implementation I wrote a while back. Using Long rather than Integer enables it to handle higher exponents:
Function mod_exp(alpha As Long, exponent As Long, modulus As Long) As Long
Dim y As Long, z As Long, n As Long
y = 1
z = alpha Mod modulus
n = exponent
'Main Loop:
Do While n > 0
If n Mod 2 = 1 Then y = (y * z) Mod modulus
n = Int(n / 2)
If n > 0 Then z = (z * z) Mod modulus
Loop
mod_exp = y
End Function
Related
i want to calculate x in this formula :
r=g^x mod n = B
and variables are :
Dim g As Double
Dim x As Double
Dim n As Double
Dim b As Double
Dim m As Double
Dim r As Double
x = 1
b = 9789467
g = 10895499
n = 16777216
m = 1
and here my codes :
Dim i As Integer
For i = 1 To 16777215
m = i
r = (g ^ m) Mod n
If r = b Then
MsgBox("result = " + i)
End If
Next
MsgBox("not found")
but , it's just works on small numbers
and with my numbers... not working :(
i would appreciate any solution guys :)
and even if u got the x value from any other languages ... it's fine :)
thank you :)
Add a reference to System.Numerics and use BigInteger
this function interpolates/extrapolates a table of known x,y
For example,
x y
1 10
2 15
3 20
Linterp(A1:B3, -1) = 0
However, this code can only do two adjacent arrays.
I would like to modify this code so that I can
select two separate arrays, for example N106:N109,P106:P109.
How can I make this adjustment in this code?
Function Linterp(r As Range, x As Double) As Double
' linear interpolator / extrapolator
' R is a two-column range containing known x, known y
Dim lR As Long, l1 As Long, l2 As Long
Dim nR As Long
'If x = 1.5 Then Stop
nR = r.Rows.Count
If nR < 2 Then Exit Function
If x < r(1, 1) Then ' x < xmin, extrapolate
l1 = 1: l2 = 2: GoTo Interp
ElseIf x > r(nR, 1) Then ' x > xmax, extrapolate
l1 = nR - 1: l2 = nR: GoTo Interp
Else
' a binary search would be better here
For lR = 1 To nR
If r(lR, 1) = x Then ' x is exact from table
Linterp = r(lR, 2)
Exit Function
ElseIf r(lR, 1) > x Then ' x is between tabulated values, interpolate
l1 = lR: l2 = lR - 1: GoTo Interp
End If
Next
End If
Interp:
Linterp = r(l1, 2) _
+ (r(l2, 2) - r(l1, 2)) _
* (x - r(l1, 1)) _
/ (r(l2, 1) - r(l1, 1))
End Function
one very simple way is having the function accepting two ranges in input, one for X values (say rX) and one for Y ones (say rY), and then changing every occurrence of r(foo,1) to rX(foo) and r(foo,2) to rY(foo)
like follows
Option Explicit
Function Linterp2(rX As Range, rY As Range, x As Double) As Double
' linear interpolator / extrapolator
' R is a two-column range containing known x, known y
Dim lR As Long, l1 As Long, l2 As Long
Dim nR As Long
'If x = 1.5 Then Stop
nR = rX.Rows.Count
If nR < 2 Then Exit Function
If x < rX(1) Then ' x < xmin, extrapolate
l1 = 1: l2 = 2: GoTo Interp
ElseIf x > rX(nR) Then ' x > xmax, extrapolate
l1 = nR - 1: l2 = nR: GoTo Interp
Else
' a binary search would be better here
For lR = 1 To nR
If rX(lR) = x Then ' x is exact from table
Linterp2 = rY(lR)
Exit Function
ElseIf rX(lR) > x Then ' x is between tabulated values, interpolate
l1 = lR: l2 = lR - 1: GoTo Interp
End If
Next
End If
Interp:
Linterp2 = rY(l1) _
+ (rY(l2) - rY(l1)) _
* (x - rX(l1)) _
/ (rX(l2) - rX(l1))
End Function
but you must implement code to check for consistency of the two ranges, like being both of one column each and with the same number of rows
use this function :
Public Function lineare_iterpolation(x As Variant, x1 As Variant, x2 As Variant, y1 As Variant, y2 As Variant) As Variant
If x = x1 Then
lineare_iterpolation = y1
Exit Function
End If
If x = x2 Then
lineare_iterpolation = y2
Exit Function
End If
lineare_iterpolation = y1 + (x - x1) * (y2 - y1) / (x2 - x1)
Exit Function
End Function
I have the following function that when I run it says #value! error.
I would appreciate any help.
Function Bootstrap(S As Object, Z As Object, L As Double)
Dim j As Integer
Dim a() As Double
Dim b() As Double
Dim n As Integer
Dim Q() As Double
Dim sum As Double
Dim P As Double
ReDim a(1 To n)
ReDim b(1 To n)
ReDim Q(1 To n)
dt = 1
sum = 0
Q(0) = 0
For j = 1 To n - 1
S.Cells(j, 1).Value = a(j)
Z.Cells(j, 2).Value = b(j)
P = Z(j) * (L * Q(j-1) - (L + dt * a(n) * Q(j))
sum = sum + P
Next j
Bootstrap = sum
End Function
Bootstrapping function calculates the following value
In fact I am trying to calculate this formula
Q(t,Tn)=(∑(j=1)to(n-1) Z(t,Tj)[LQ(t,Tj-1)-(L+dtSn)Q(t,Tj)]/[Z(t,Tn)(L+dt*Sn)] +(Q(t,Tn-1)L)/(L+dtSn)
Inputs given are[S1 ,S2,….Sn ],[Z(t,T1),Z(t,T2)…..Z(t,Tn)]and and L=0.4
Try this code : entered as =Bootstrap(A1:B1,A2:B2,0.4)
I have corrected the following
- Assigning the ranges to variants
- defining dt as double
- Dim Q() as 0 to n
- using A() and b() in the formula
- the input ranges are rows not columns
Function Bootstrap(S As Range, Z As Range, L As Double) As Double
Dim j As Integer
Dim a As Variant
Dim b As Variant
Dim n As Integer
Dim Q() As Double
Dim sum As Double
Dim P As Double
Dim dt As Double
n = Application.WorksheetFunction.Max(S.Columns.Count, Z.Columns.Count)
a = S.Value
b = Z.Value
dt = 1
sum = 0
ReDim Q(0 To n)
Q(0) = 0
For j = 1 To n - 1
P = b(1, j) * (L * Q(j - 1)) - (L + dt * a(1, j) * Q(j - 1))
sum = sum + P
Q(j) = sum
Next j
Bootstrap = sum
End Function
Take the habit to format and increment your code, especially before posting it!
You need to type the output of the function (on the line of the function name)
A parenthesis is missing from the line P = Z(j) * (L*Q(j-1)-(L+ dt * a(n) * Q(j))
n is empty (and so are a, b and Q) when you try to redim your arrays, so you need to define them!
Z(j) will also give you an error, because it is a Range, you need Z.Cells(i,j)
Try this :
Function Bootstrap(S As Range, Z As Range, L As Double) As Double
Dim j As Integer
Dim a() As Double
Dim b() As Double
Dim n As Integer
Dim Q() As Double
Dim sum As Double
Dim P As Double
n = Application.WorksheetFunction.Max(S.Columns.count, Z.Columns.count)
a = S.Value
b = Z.Value
dt = 1
sum = 0
ReDim Q(1 To n)
Q(0) = 0
'Q(1) = "??"
For j = 1 To n - 1
P = b(1, j) * (L * Q(j - 1)) - (L + dt * a(1, j) * Q(j - 1))
sum = sum + P
Q(j) = sum
Next j
Bootstrap = sum
End Function
I have a list of distances that I would like to display like you would read off a tape measure, for example 144.125 would display as 144 1/8". I have the following formula
=TEXT(A1,"0"&IF(ABS(A1-ROUND(A1,0))>1/32,"0/"&CHOOSE(ROUND(MOD(A1,1)*16,0),16,8,16,4,16,8,16,2,16,8,16,4,16,8,16),""))&""""
I'd like to simplify it to a 1 argument function (for A1) so I could use it throughout the workbook, but the amount of " quotes and vba keywords is causing problems. Is there an easier way to get a UDF to insert a complicated formula?
If you want to use a UDF with visual basic then try this:
Public Function Fraction(ByVal x As Double, Optional ByVal tol As Double = 1 / 64#) As String
Dim s As Long, w As Long, d As Long, n As Long, f As Double
s = Sgn(x): x = Abs(x)
If s = 0 Then
Fraction = "0"
Exit Function
End If
w = CInt(WorksheetFunction.Floor_Precise(x)): f = x - w
d = CInt(WorksheetFunction.Floor_Precise(1 / tol)): n = WorksheetFunction.Round(f * d, 0)
Dim g As Long
Do
g = WorksheetFunction.Gcd(n, d)
n = n / g
d = d / g
Loop While Abs(g) > 1
Fraction = Trim(IIf(s < 0, "-", vbNullString) + CStr(w) + IIf(n > 0, " " + CStr(n) + "/" + CStr(d), vbNullString))
End Function
With results:
The TEXT function can do this directly:
A B
1 144,1250 144 1/8 "
Formula in B1:
=TEXT(A1;"# ??/??\""")
Greetings
Axel
this application for computing the gcd by using extended euclidean but it give me just the value for first iteration but i need the final values of x2 y2 a
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim x1 As Integer
Dim x2 As Integer
Dim y1 As Integer
Dim y2 As Integer
Dim x As Integer
Dim y As Integer
Dim a As Integer
Dim temp As Integer
a = CInt(TextBox1.Text)
Dim b As Integer
b = CInt(TextBox2.Text)
Dim q As Integer
x1 = 0
y1 = 1
x2 = 1
y2 = 0
If b > a Then
temp = a
a = b
b = temp
End If
Do While (b <> 0)
q = Math.Floor(a / b)
a = b
b = a Mod b
x = x2 - q * x1
x2 = x1
y = y2 - q * y1
y2 = y1
x1 = x
y1 = y
Loop
MessageBox.Show("the final value of x2 is " & CStr(x2) & "the final value of y2 is " & CStr(y2) & "the GCD is " & CStr(a), " the result ")
End Sub
Here's your problem:
a = b
b = a Mod b
In the second statement, a is already equal to b, so a Mod b is always zero.
'Euclid's algorithm
'code assumes that you are looking for the GCD of the
'values entered into TextBox1 and TextBox2
Dim dividend As Long
Dim divisor As Long
Dim quotient As Long
Dim remainder As Long
If Long.TryParse(TextBox1.Text, dividend) Then
If Long.TryParse(TextBox2.Text, divisor) Then
'place in correct order
quotient = Math.Max(dividend, divisor) 'determine max number
remainder = Math.Min(dividend, divisor) 'determine min number
dividend = quotient 'max is dividend
divisor = remainder 'min is divisor
Do
quotient = Math.DivRem(dividend, divisor, remainder) 'do the division
'set up for next divide
dividend = divisor 'dividend is previous divisor. if remainder is zero then dividend = GCD
divisor = remainder 'divisor is previous remainder
Loop While remainder <> 0 'loop until the remainder is zero
Label1.Text = dividend.ToString("n0")
End If
End If