Hi VT

The use of LastValue(N+PREV-PREV) (as used in the adaptive functions of MS11) will generally give you this capability. However it's a resource-intensive method and not totally accurate . My March special issue of MSTT gives replacement code for around 75% of the adaptive functions, mostly without speed or accuracy issues. I have yet to work though one or two issues with another three or four adaptive functions but already have solutions for many other functions not included in the MS11 adaptive group.

Roy

Hi VT

Adding a non-PREV variable Periods capability to some functions such as most of those included in the Forum DLL is quite easy. For example, ExtFml("Forum.MOV",Data,Periods,Method) works pretty much as expected when supplied with a variable Periods parameter. However the Aroon function doesn’t get it quite right so assuming "N" is your Periods parameter you might instead try this.

{Aroon Up / Aroon Down}

N:=N+(N=0); {prevents an illegal Periods value of zero}

U:=100*(N-ExtFml("Forum.HHVBars",H, N+1))/N;

D:=100*(N-ExtFml("Forum.LLVBars",L, N+1))/N;

ValueWhen(1,N>0,U); ValueWhen(1,N>0,D);

This code also uses the Forum DLL but not its Aroon function which is "slightly off".

Roy

Hi VT

What's happening here is that your formula takes a constant, presumably a periods value entered via an Input() function, and then converts it to a variable (as far as MetaStock is concerned) when calculating the square root. The LastValue() fction converts the "variable" back to a constant which is why your formula still works when +PREV-PREV is removed.

It doesn't matter where the LastValue() function is applied to the offending variable. It can be in the line that performs the square root or it can be placed inside the Mov() function.

Not only does LastValue() supply the last value of any data array, it also converts any calculated fixed value so that it can be recognised as a constant by MetaStock. Once you perform any calulation on a constant it will be considered as a variable by MetaStock. Perhaps an exception to this is where two constants are added or multiplied - an example being that 10+3 will be trated as a legitimate constant of 13 if used as a Periods parameter in any function.

When LastValue() is used in conjunction with a variable and +PREV-PREV, the PREV component is self-cancelling (zero) but the presence of PREV forces the variable result to be recalculated on every bar, and LastValue() forces that recalculated result to be returned to MetaStock as a "constant", albeit a constant that can change on each bar. As it turns out LastValue(N+PREV-PREV) is not necessary for your formula because N is always the same value and just using LastValue() has the desired effect of making MetaStock accept it as a constant. Where N is a changing or adaptive value you would need to use the +PREV-PREV element for Mov() to accept the "variable" parameter.

Roy