Re: UnitStep

*To*: mathgroup at smc.vnet.net*Subject*: [mg52334] Re: [mg52326] UnitStep*From*: DrBob <drbob at bigfoot.com>*Date*: Wed, 24 Nov 2004 02:32:05 -0500 (EST)*References*: <200411230712.CAA29371@smc.vnet.net>*Reply-to*: drbob at bigfoot.com*Sender*: owner-wri-mathgroup at wolfram.com

(1/0)*0 is undefined in Mathematica, just as it should be. You can define the function this way, however: (inputs) f[p_] = If[p == 0, 0, (1/p) UnitStep[p - 1]]; Integrate[f@x, {x, -5, 5}] D[f@x, {x}] Integrate[%, x] Plot[f@x, {x, -5, 5}] (outputs) Log[5] If[x == 0, 0, DiracDelta[x - 1]/ x - UnitStep[x - 1]/x^2] Integrate[If[x == 0, 0, DiracDelta[x - 1]/x - UnitStep[x - 1]/x^2], x] (and a plot) D followed by Integrate is unevaluated. In version 5.1 we have a different choice: (inputs) f[p_] = Piecewise[{{0, p == 0}, {(1/p) UnitStep[p - 1], True}}]; Integrate[f@x, {x, -5, 5}] D[f@x, {x}] Integrate[%, x] Plot[f@x, {x, -5, 5}] (outputs) Log[5] Piecewise[{{0, x < 1}, {-(1/x^2), x > 1}}, Indeterminate] Piecewise[{{0, x <= 1}}, -1 + 1/x] (and a plot) This time D followed by Integrate is evaluated, but WRONG. Bobby On Tue, 23 Nov 2004 02:12:45 -0500 (EST), Blimbaum, Jerry AA R22 <jerry.blimbaum at navy.mil> wrote: > Why does the following give me 'indeterminate, infinite expression > encountered', etc. instead of zero.... > > > (1/p) UnitStep[p-1] /.p->0 > > > I defined a function using the UnitStep because p could = 0 and I > thought this would be the way around that problem.......but didnt work > the way I expected..... > > > jerry blimbaum > > > > > -- DrBob at bigfoot.com www.eclecticdreams.net

**References**:**UnitStep***From:*"Blimbaum, Jerry AA R22" <jerry.blimbaum@navy.mil>