Bill Williams Averages SMMA

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//  Copyright by HPotter v2.0 24/09/2014
// This indicator calculates 3 Smoothed moving average for default values of
// 13, 8 and 5 days, with displacement 8, 5 and 3 days: Median Price (High+Low/2).
// The most popular method of interpreting a moving average is to compare 
// the relationship between a moving average of the security's price with 
// the security's price itself (or between several moving averages).
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study(title="Bill Williams Averages. 3Lines", shorttitle="3 Lines", overlay = true)
LLength = input(13, minval=1)
MLength = input(8,minval=1)
SLength = input(5,minval=1)
LOffset = input(8,minval=1)
MOffset = input(5,minval=1)
SOffset = input(3,minval=1)
SUM1 = sum(close, LLength)
SMMA1 = SUM1/LLength
PREVSUM1 = SMMA1[1] * LLength
SMMAL = (PREVSUM1-nz(SMMAL[1])+close)/LLength
SUM2 = sum(close, MLength)
SMMA2 = SUM2/MLength
PREVSUM2 = SMMA2[1] * MLength
SMMAM = (PREVSUM2-nz(SMMAM[1])+close)/MLength
SUM3 = sum(close, SLength)
SMMA3 = SUM3/SLength
PREVSUM3 = SMMA3[1] * SLength
SMMAS = (PREVSUM3-nz(SMMAS[1])+close)/SLength
plot(SMMAL[LOffset], color=blue, title="SMMA L")
plot(SMMAM[MOffset], color=red, title="SMMA M")
plot(SMMAS[SOffset], color=green, title="SMMA S")