Accumulation Swing Index [ASI]

Summary:
This indicator script is used to measure long term trends.

Calculation:
The cumulative total of the swing index, which attempts to show the real price of the underlying symbol.

Developer:
J. Welles Wilder, jr.

Interpretation: 
1. Upwards Trend: When the indicator script is moving upwards, the underlying symbol is in an upwards trend.
2. Downwards Trend: When the indicator script is moving downwards, the underlying symbol is in a downwards trend.
3. Upwards Momentum: When the indicator script is positive and moving upwards, the underlying symbol has upwards momentum and is likely to continue moving upwards.
4. Downwards Momentum: When the indicator script is negative and moving downwards, the underlying symbol has downwards momentum and is likely to continue moving downwards.
5. Positive Divergence:  When the underlying symbol is moving downwards, but the indicator script is moving upwards, the underlying symbol is likely to reverse direction and move upwards.
6. Negative Divergence:  When the underlying symbol is moving upwards, but the indicator script is moving downwards, the underlying symbol is likely to reverse direction and move downwards.

	 ' Initialize the indicator as an index indicator.
	IndicatorIndex(symbolIndex)
	 ' Assign the parameters to script variables.
	_symbolIndex = symbolIndex
	_limitMove = limitMove

	 ' Get the opening prices of the underlying symbol, indexed by bar index.
	Define open() As Number = BarOpen(_symbolIndex, barIndex, length + 1)
	 ' Get the highest prices of the underlying symbol, indexed by bar index.
	Define high() As Number = BarHigh(_symbolIndex, barIndex, length + 1)
	 ' Get the lowest prices of the underlying symbol, indexed by bar index.
	Define low() As Number = BarLow(_symbolIndex, barIndex, length + 1)
	 ' Get the closing prices of the underlying symbol, indexed by bar index.
	Define close() As Number = BarClose(_symbolIndex, barIndex, length + 1)
	 ' Get the volume values of the underlying symbol, indexed by bar index.
	Define volume() As Number = BarVolume(_symbolIndex, barIndex, length + 1)
	 ' Get the last Accumulation Swing Index value.
	Define ASI As Number = IndicatorIndexValue()
	 ' Use for various calculations.
	Define swingIndex,upper,R,K,R1,R2,R3,R4 As Number
	
	 ' Use for the calculated Accumulation Swing Index values, indexed by bar index.
	Define results(length - 1) As Number
	 ' Calculate the Accumulation Swing Index values for the specified bar range.
	For i As Integer = length - 1 To 0 Step -1
		 ' Calculate the Accumulation Swing Index value for the current bar.
		If (close(i+1) <> 0) Then
			upper = (close(i) - close(i+1)) + 0.5 * (close(i) - open(i)) + 0.25 * (close(i+1) - open(i+1))
			R1 = MathAbs(high(i) - close(i+1))
			R2 = MathAbs(low(i) - close(i+1))
			R3 = MathAbs(high(i) - low(i))
			R4 = MathAbs(close(i+1) - open(i+1))
			If (R1 >= MathMax(R2, R3)) Then
				R = R1 - (R2 / 2) + (R4 / 4)
			Else If (R2 >= MathMax(R1,R3)) Then
				R = R2 - (R1 / 2) + (R4 / 4)
			Else
				R = R3 + (R4 / 4)
			End If
			K = MathMax(R1,R2)
			If (R <> 0) Then
				swingIndex = (50 * (upper / R) * K) / _limitMove
				If (-100 <= swingIndex And swingIndex <= 100) Then
					ASI += swingIndex
				Else If (swingIndex > 100) Then
					ASI += 100
				Else
					ASI += -100
					ASI += swingIndex
				End If
			End If
		End If
		 ' Assign the Accumulation Swing Index value for the current bar.
		results(i) = ASI
	Next
	Return results