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From: cwldoc on 18 Jun 2010 14:02
> On Thu, 17 Jun 2010 21:15:56 -0700, Tim Foe wrote:
>
> [top posting corrected]
>
> >On Jun 17, 6:20pm, James Waldby wrote:
> >> On Thu, 17 Jun 2010 13:04:55 -0700, Tim Foe wrote:
> >> > I'm looking for a simple way to describe the
> following function:
> >> > 10
> >> > 1
> >> > .1
> >> > .01
> >> > .001
> >> > 0
> >> > -.001
> >> > -.01
> >> > -.1
> >> > -1
> >> > -10
> >> > it's sort of like a sigmoid but rotated
> ...
> >> Anyhow, if those are readings y_i taken at times
> x_i with
> >> delta x constant, then the semi-log graph of
> abs(y_i) vs x_i
> >> is slightly reminiscent of a chevron plot, as seen
> at
> >> <http://en.wikipedia.org/wiki/Chevron_plot>
> >
> >sorry, i need a function that relates an array such
> as:
> >
> >from 1 to 10
> >
> >or
> >
> >from 0.1 to 1 step .1
> >
> >to the array i listed originally
>
> Please don't top post. I've moved your text to the
> end.
>
> You could try -signum(x-5) * 10^{ abs(x-5)-3 }, where
> signum
> and abs are as at
> <http://en.wikipedia.org/wiki/Sign_function>
> and <http://en.wikipedia.org/wiki/Absolute_value>.
>
> --
> jiw
>

How about
f(x) = 10^(x-4), for x < 0
f(x) = 0, for x = 0
f(x) = -(10^(4-x)), for x > 0
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