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do we need to be moderated? Re: Piecewise Functions
Posted:
Aug 16, 1996 3:01 AM


This this question was asked so long ago that its expired and I cant even remember what the question was. No offense, I'm sure moderating its alot of work, but if you are going on vacation or something cant you temporatily let everything pass through?
:> i'm stumped... : :You can approximate the derivative numerically by using a function such as: : :fderiv[x_]:=(f[x]f[x0.001] )/0.001 : :It might not be elegant, but it works.
as I recall, the problem is that for a pievewise function:
f[x_ /; x> 0] := g[x] f[x_ /; x<=0] := h[x]
differentiation doesn't work correctly even where we specify the point x:
D[f[x],x] /. x> 1 f'[1]
the best I could come up with is to define the derivates piecewise as well:
f'[x_ /; x>0 ] := D[g[y],y] /. y>x f'[x_ /; x<0 ] := D[h[y],y] /. y>x
D[f[x],x] /. x> 1
g'[1]
This doesn't look too bad for this simple example but its still a real mess where you have multiple derivateves and more complicated functions..



