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Topic: changing variable in an equation
Replies: 4   Last Post: Feb 13, 2011 5:51 AM

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Albert Retey

Posts: 688
Registered: 7/15/08
Re: changing variable in an equation
Posted: Feb 13, 2011 5:51 AM
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Hi,

> Those that have responded have requested further information. I hope this
> will help.
>

...
> What I tried to do was to just plot his solution which is V(t)= Vsubnl + (V0
> - Vsubnl)times e to the -gsubL * t divided by c. What I did was make up
> different equations such as vt1 = -67+(0-(-67))*e^-19t/c and substitute
> values for t. And then make another equation with a different V0 and do the
> same thing. Then finally combine them using Plot{{vt1,vt2 and so on},
> {t,0,5}].
>
> These results mimic his plots so I am on the right track. It's just that my
> way takes an enormous amount of time. I know that there must be a better
> way to do this with Mathematica. That's the whole point of my request for
> help.


I'm not sure whether I got what you want and don't have the book to
check, but I think the following should be a starting point to achieve
what you probably want:

sol = VsubnL + (V0 - VsubnL)*E^(-gsubL*t/c)

parameters = {c -> 10, gsubL -> 19, VsubnL -> -67}

Plot[Evaluate[Table[sol /. parameters, {V0, 0, 100, 20}]], {t, 0,
5}, Frame -> True, Axes -> False, PlotRange -> All,
ImageSize -> 500]

hth,

albert




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