Re: Evaluating UnitStep inside another function
- To: mathgroup at smc.vnet.net
- Subject: [mg16296] Re: Evaluating UnitStep inside another function
- From: Doug Webb <Douglas.S.Webb at maf.nasa.gov>
- Date: Sun, 7 Mar 1999 01:05:32 -0500
- Organization: http://www.msfc.nasa.gov/
- References: <7bo033$dnr@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Hello,
I fixed this one and thought I'd let any interested parties know. By
changing the attributes of UnitStep to include Listable, it works fine. Just
Unprotect, SetAttributes, and re Protect.
Doug
Doug Webb wrote:
> Hello,
> I am trying to define a function such as this, where lst and xvlu have
> already been defined earlier as lists (which the user wont really know
> about or be able to see):
>
> lst = {1, 2, 3}
> xvlu = {0, 2, 5}
>
> F1[ func_, var_ ] := (
> lst = func /. var -> xvlu;
> Return[ lst ]
> );
>
> And func can be any arbitrary function the user wants to enter, which is
> based on variable var. This all works fine for cases such as this:
>
> F1[ x^2, x ]
>
> returns:
>
> {0, 4, 25}
>
> What I'm having problems with is the UnitStep function. After loading
> the DiracDelta package:
>
> <<Calculus`DiracDelta`
>
> The following input
>
> F1[ 3 + UnitStep[ x-3 ], x ]
>
> Gives this output:
>
> 3 + UnitStep[ {-3, -1, 2} ]
>
> Rather than what I want:
>
> {3, 3, 4}
>
> If I enter it directly as this:
>
> 3 + UnitStep[ xvlu - 3 ]
>
> then I get the "correct" answer of {3, 3, 4}. Evidently the UnitStep
> isn't getting evaluated inside the F1[] function. I've tried
> combinations of Evaluate[], Hold[], N[], etc. in all they ways I can
> think of inside the F1[] function, and still no luck. What can I do
> inside F1[] to get the UnitStep case evaluated, without possible
> "messing up" a simpler case with something like x^2? Thanks for any
> suggestions.
>
> Doug
> Douglas.S.Webb at maf.nasa.gov
> D_Webb at prodigy.net