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Topic: Equation for controlled fade
Replies: 1   Last Post: Oct 23, 2006 1:57 PM

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Lynn Kurtz

Posts: 1,278
Registered: 12/6/04
Re: Equation for controlled fade
Posted: Oct 23, 2006 1:57 PM
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On 23 Oct 2006 03:00:21 -0700, "Nick" <Nick.Stansbury@googlemail.com>
wrote:

>Hi,
>
> I'm sure I'm being dumb but I can't think of a way to solve this. Any
>help appreciated.
>
>Given three given values of "Start", "End" and "Length", I need a
>function for variables time "T" and values "X" where at T = 1 X=Start
>and at T=Length X=End. However if you graph T and X (T along the Y axis
>and X along the X axis) I'd like the graph to look something like the
>graph of 1/X, i.e. an exponential like "fade" from Start to End over T
>periods.
>
>Hope this makes sense - any ideas appreciated!
>
>Nick


1/x is not an "exponential". Using the letters:

l = length
s = start
e = end
x = X
t = T

try the equation: t = l^( ( x - s) / ( e - s ) )

When x = s you get l^0 = 1 and when x = e you get l^1 = l.

(Here e is just a variable, not the standard calculus e.)

--Lynn



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