       Re: Plot problem

• To: mathgroup at smc.vnet.net
• Subject: [mg61588] Re: [mg61578] Plot problem
• From: Bob Hanlon <hanlonr at cox.net>
• Date: Sun, 23 Oct 2005 05:45:52 -0400 (EDT)
• Sender: owner-wri-mathgroup at wolfram.com

```If you use capital letters for your variables they will get confused with
Mathematica definitions, e.g., E has a definition

N[E]

2.71828

Clear[r];
r[a_,b_,c_,d_,e_,x_]:=Evaluate[r/.Solve[
{lamda==Sqrt[r*a*x/b],r==c *x *(d+e/lamda)},
r,lamda][]//Simplify];

r[a,b,c,d,e,x]

(1/6)*((2*2^(1/3)*a*c^2*d^2*x^2)/(-2*a^3*c^3*d^3*x^3 +
27*a^2*b*c^2*e^2*x +
3*Sqrt*Sqrt[a^4*b*c^4*e^2*x^2*(27*b*e^2 - 4*a*c*d^3*x^2)])^(1/3)
+ 4*c*d*x +
(2^(2/3)*(-2*a^3*c^3*d^3*x^3 + 27*a^2*b*c^2*e^2*x +
3*Sqrt*Sqrt[a^4*b*c^4*e^2*x^2*(27*b*e^2 - 4*a*c*d^3*x^2)])^
(1/3))/a)

To plot, you will need to assign values to the constants.

Module[
{a=4,b=1,c=3,d=7,e=9,ineq,x1,x2},
ineq=Reduce[{
Sqrt[a^4*b*c^4*e^2*x^2*(27*b*e^2-4*a*c*d^3*x^2)]>0,
(-2*a^3*c^3*d^3*x^3+27*a^2*b*c^2*e^2*x+3*Sqrt*
Sqrt[a^4*b*c^4*e^2*x^2*(27*b*e^2-4*a*c*d^3*x^2)])>0},
x,Reals];
x1=ineq[];
x2=ineq[];
Plot[r[a,b,c,d,e,x],{x,x1,x2}]];

Bob Hanlon

>
> From: "smilehezuk" <smilehezuk at gmail.com>
To: mathgroup at smc.vnet.net
> Date: 2005/10/22 Sat AM 05:11:24 EDT
> Subject: [mg61588] [mg61578] Plot problem
>
> Hi everyone!
>
> I want to solve these equations and plot. Please tell me how.
>
> There are two equations;
>
> Lamda = Sqrt[R A x/B], R = C x (D + E/Lamda)
> (A,B,C,D,E : constants, x : another variable)
>
> I need to plot R versus x.
>