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

Groups > comp.soft-sys.math.mathematica > #2807

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

Show all headers | View raw

The derivative of the function you provided is very complicated and I'd be surprised if a symbolic solution to the equation is possible. Since you didn't provide any numerical values for the constants (l1, l2, v1, v2, c, L1, L2, V1, V2, C), there's not much Mathematica can do.

However, I have to wonder if you intended to have two sets of constants (lower-case and upper-case)? If not, then replacing the upper-case constants with the lower-case constants yields an answer:

In[156]:= f = ((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)) /. {L1 -> l1,
   L2 -> l2, V1 -> v1, V2 -> v2, C -> c}

Out[156]= (2 (l2 (1 - x) + l1 x))/(v2 (1 - x)^2 + 2 c (1 - x) x + v1 x^2)^0.5

In[157]:= Solve[D[%, x] == 0, x]

Out[157]= {{x -> (1. c l2 - 1. l1 v2)/(1. c l1 + 1. c l2 - 1. l2 v1 - 1. l1 v2)}}

David

Back to comp.soft-sys.math.mathematica | Previous | Next | Find similar | Unroll thread

Thread

Re: Simple question: is it possible to take a derivative and solve for x ? David Skulsky <edskulsky@gmail.com> - 2011-05-30 10:36 +0000

csiph-web