The indicator logic is described in the January issue of TASC and sounds intriguing. Without rehashing the details of the indicator calculation, it is very similar to Welles Wilder’s Directional Movement Index Calculation (DMI) except that Wilder’s Directional Movement (largest part of today’s range outside of yesterday’s range) is replaced by calculating the differences between today’s High and yesterday’s Low (positive Vortex Movement) and today’s Low and yesterday’s High (negative Vortex Movement).

Go long when the VI (or Dmi) goes from less than zero to greater than zero.
Go short when the VI (or Dmi) goes from above zero to less than zero.


period = Param("Period", 14, 2 ); 

VMP = Sum( abs( H - Ref( L, -1 ) ), period ); 
VMM = Sum( abs( L - Ref( H, -1 ) ), period ); 
STR = Sum( ATR( 1 ), period ); 

VIP = VMP / STR; 
VIM = VMM / STR; 

Plot( VIP, "VI"+period+"+", colorBlue); 
Plot( VIM, "VI"+period+"-", colorRed );