Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.soft-sys.math.mathematica > #2790 > unrolled thread

Re: Simple question: is it possible to take a derivative and solve for x ?

Back to article view | Back to comp.soft-sys.math.mathematica

Contents

  Re: Simple question: is it possible to take a derivative and solve for x ? Robert Rosenbaum <robertr@math.uh.edu> - 2011-05-30 10:34 +0000

#2790 — Re: Simple question: is it possible to take a derivative and solve for x ?

First, you seem to have used the reserved variable C as a parameter.  You should rename it.

Second, it's highly unlikely that a closed form solution exists.

If you want to find the solutions, you'll have to instantiate the parameters and solve for each instantiation.  For instance:

NSolve[(D[((x*l1 + (1 - x)*
           l2)/((x^2*v1 + (1 - x)^2*v2 + 2*x*(1 - x)*c)^0.5)) + ((x*
           L1 + (1 - x)*
           L2)/((x^2*V1 + (1 - x)^2*V2 + 2*x*(1 - x)*cc)^0.5)), x] == 0)
 /. {l1 -> 2, l2 -> 3, v1 -> 7, v2 -> 8, c -> 4, L1 -> 3, L2 -> 6, V1 -> 5, V2 -> 13, cc -> 3},
x]

gives three solutions, one of which is real.  Note that I changed your variable C to cc.


Best,
Robert


On May 29, 2011, at 6:36 AM, Alonso wrote:

> I am a beginner, and would like to know if it is possible to solve for x the first derivative of a long equation in Mathematica. Bear with me, my background is in Biomedical Sciences.
>
> I am typing the following command:
>
> Solve[D[((x*l1 + (1 - x)*l2)/((x^2*v1 + (1 - x)^2*v2 +  2*x*(1 - x)*c)^0.5))+((x*L1 + (1 - x)*L2)/((x^2*V1 + (1 - x)^2*V2 +  2*x*(1 - x)*C)^0.5)), x]==0,x]
>
> But Mathematica 8 simply stops, and no output is given.
>
> Any tips?
>
> Cheers!
>
> Alonso
>

[toc] | [standalone]

Back to top | Article view | comp.soft-sys.math.mathematica

csiph-web