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MathGroup Archive 2001

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Re: making a function of two coordinates

  • To: mathgroup at
  • Subject: [mg31638] Re: [mg31617] making a function of two coordinates
  • From: Anton Antonov <antonov at>
  • Date: Mon, 19 Nov 2001 03:11:22 -0500 (EST)
  • Sender: owner-wri-mathgroup at

	Hi Roderik,
	First for the exponential you can use the Mathematica build-in
function Exp[]. Also, equations in Mathematica are defined in with ==.
So this is OK:

In[1]:= Clear[U, e, a, t, y]
        Solve[y == U*Exp[a*t], a]

Out[1]:={{a -> Log[y/U]/t}}

	I used Clear[] because y = U*e^(a*t) sets a value to y.
(Try to evaluate  y = U*e^(a*t) first and then Solve[y == U*e^(a*t), a],
and you will see that nothing happens.) If you try

In[2]:= Solve[y == U*e^(a*t), a]

you will get

Out[2]:= {{a -> Log[y/U]/(t*Log[e])}}

since Mathematica doesn't know what e is.


Anton Antonov Antonov, PhD     *****     Wolfram Research Inc.   ***   tel +1 217 398 0700 #782
               Give me wings and I will crawl faster!

On Sun, 18 Nov 2001, TheSquaredBun wrote:

> I have got two coordinates out of graph. The line through the
> coordinates could be described as:
> y = U * e^(a * t)
> (e is Exponetial e (approx. 2.37))
> t is the x-value, I have give two points (t1,y1) and (t2,y2)
> I have tried several things (Solve and Fit for example), but I can't
> get the function.
> Does anyone know what should be the input to let Mathematica solve the
> a and U in the formula.
> Much thanks in advance,
> Roderik
> r.f.emmerink at

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