Cumulative Volume Index [CVI]

Summary:
This indicator script measures market momentum to illustrate money flows in and out of an exchange.

Calculation:
The cumulative difference between the volumes of advancing and declining symbols of the specified exchange.

Developer:
Steven B. Achelis

Interpretation:
1. Upwards Trend: When the indicator script is moving upwards, the underlying exchange is in an upwards trend.
2. Downwards Trend: When the indicator script is moving downwards, the underlying exchange is in a downwards trend.
3. Positive Divergence:  When the underlying exchange is moving downwards, but the indicator script is moving upwards, the underlying exchange is likely to reverse direction and move upwards.
4. Negative Divergence:  When the underlying exchange  is moving upwards, but the indicator script is moving downwards, the underlying exchange is likely to reverse direction and move downwards.

	 ' Assign the parameter to a script variable and make sure it is in upper case.
	_exchangeID = StringToUpper(exchangeID)
	 ' Find a symbol index that matches the specified exchange ID.
	Define symbolIndex As Integer = -1
	For i As Integer = 0 To SymbolCount() - 1
		If (SymbolExchangeID(i) = _exchangeID)
			symbolIndex = i
		End If
	Next
	 ' Initialize the indicator index.
	IndicatorIndex(symbolIndex)

	 ' Use for the volume of advancing symbols, indexed by bar index. 
	Define advancing(length - 1) As Integer
	 ' Use for the volume of declining symbols, indexed by bar index.
	Define declining(length - 1) As Integer
	 ' Use for the calculated indicator values, indexed by bar index.
	Define results(length - 1) As Number
	 ' Iterate over all of the symbols in the group.
	For symbolIndex As Integer = 0 To SymbolCount() - 1
		 ' Only process symbols that belong to the specified exchange.
		If (SymbolExchangeID(symbolIndex) = _exchangeID) Then
			 ' Get the opening prices of the current symbol, indexed by bar index.  
			Define open() As Number = BarOpen(symbolIndex, barIndex, length)
			 ' Get the closing prices of the current symbol, indexed by bar index. 
			Define close() As Number = BarClose(symbolIndex, barIndex, length)
			 ' Get the volume of the current symbol, indexed by bar index.  
			Define volume() As Number = BarVolume(symbolIndex, barIndex, length)
			 ' Iterate over all of the symbol bars while counting the advancing and declining volumes.
			For i As Integer = length - 1 To 0 Step -1
				If (close(i) > open(i)) Then
					advancing(i) += volume(i)
				Else If (close(i) < open(i)) Then
					declining(i) +=  volume(i)
				End If
			Next
		End If
	Next

	Define indexValue As Number = IndicatorIndexValue()
	 ' Calculate the Cumulative Volume Index values for the specified bar range.
	For i As Integer = length - 1 To 0 Step -1
		 ' Calculate the Cumulative Volume Index value for the current bar.
		indexValue = indexValue + (advancing(i) - declining(i))
		results(i) = indexValue
	Next
	Return results