Simplying linear equation to get quartic in q using Maple

[wel]

Using the maple I am trying to get quardic in q from this big linear equation. Then use Descarte’s rule of signs to determine the number of positive roots.
\begin{equation}
\frac{\gamma*q*P_Q}{k_p*(1-q)*P_C} = \frac{I*\alpha}{k_f+k_d+\frac{k_n*\lambda_b*\gamma*q*P_Q}{\lambda_b* \gamma *q*P_Q+k_p*\lambda_r*(1-q)^2}+k_p*(1-q)}
\end{equation}
Values of parameters are given below:
I=1200
k_f = 6.7*10.^7
k_d = 6.03*10.^8
k_n = 2.92*10.^9
k_p = 4.94*10.^9
[itex]\alpha = 1.14437*10.^(-3)[/itex]
[itex]\lambda_b = 0.87e-2[/itex]
[itex]\lambda_r = 835[/itex]
[itex]\gamma = 2.74[/itex]
P_C = 3*10.^(11)
P_Q = 2.87*10.^(10)

=>
I tried the code in maple to get quartic in q but does not works. II := 1200:
k_f := 6.7*10.^7:
k_d := 6.03*10.^8:
k_n := 2.92*10.^9:
k_p := 4.94*10.^9:
alpha := 1.14437*10.^(-3):
lambda_b := 0.87e-2:
lambda_r := 835:
ggamma := 2.74:
P_C := 3*10.^11:
P_Q := 2.87*10.^10:

eq := ggamma*q*P_Q/(k_p*(1-q)*P_C) = II*alpha/(k_f+k_d+k_n*lambda_b*ggamma*q*P_Q/(lambda_b*ggamma*q*P_Q+k_p*lambda_r*(1-q)^2)+k_p*(1-q)):

simply(eq, q);My lecturer want me to manipulate the equation and get a quartic in q before substituting the values of parameters into the equation. After that,use Descarte’s rule of signs to determine the number of positive roots. Then write Q=1-q to get second quartic in Q and repeat rule of signs to determine number of steady states of q less than 1. And do the substition of parameters if necessary.
Now, its kind of hard for me what he wants because to get quartic in q first from the equation is hard to do by hand , so i have to use in maple which is not working then use Descarte’s rule of signs.

 

[donpacino]

first get the equation in the form of

[itex]\frac{A_{1}*q^{1}+A_{2}*q^{2}+...A_{n}*q^{n} }{ B{1}*q^{1}+B_{2}*q^{2}+...B_{n}*q^{n} }[/itex]

to do this, simply multiple both the numerator and denominator by λb∗γ∗q∗PQ+kp∗λr∗(1−q)2

 

[wel]

first get the equation in the form of

[itex]\frac{A_{1}*q^{1}+A_{2}*q^{2}+...A_{n}*q^{n} }{ B{1}*q^{1}+B_{2}*q^{2}+...B_{n}*q^{n} }[/itex]

to do this, simply multiple both the numerator and denominator by λb∗γ∗q∗PQ+kp∗λr∗(1−q)2

multiply both numerator and denominator by λb∗γ∗q∗PQ+kp∗λr∗(1−q)2 in both sides?

 

[The Electrician]

I'm not familiar with Maple, but in Mathematica there are two commands useful for this sort of thing.

Apart[] performs a partial fraction decomposition.

Together[] combines terms into a single fraction.

Maple no doubt has similar commands.

Here's what I get by combining terms:

Now you can collect powers in the numerator and denominator to get the form suggested by donpacino.

 

[wel]

If i divide top and bottom by [itex]{\lambda_b* \gamma *q*P_Q+k_p*\lambda_r*(1-q)^2}[/itex] then i get:

\begin{equation}
\frac{\gamma*q*P_Q}{k_p*(1-q)*P_C} = \frac{(I*\alpha)(\lambda_b* \gamma *q*P_Q+k_p*\lambda_r*(1-q)^2)} {(k_f+k_d+k_p*(1-q))(\lambda_b* \gamma *q*P_Q+k_p*\lambda_r*(1-q)^2)+k_n*\lambda_b*\gamma*q*P_Q}
\end{equation}
and then doing cross multiplying gives

\begin{equation}
[(k_f+k_d+k_p*(1-q))(\lambda_b* \gamma *q*P_Q+k_p*\lambda_r*(1-q)^2)+k_n*\lambda_b*\gamma*q*P_Q]*(\gamma*q*P_Q) = (I*\alpha)(\lambda_b* \gamma *q*P_Q+k_p*\lambda_r*(1-q)^2)(k_p*(1-q)*P_C)
\end{equation}
now i guess from there maple can help me to simple the expression to get quartic in q but maple is not simplying it.

 

[donpacino]

multiply both numerator and denominator by λb∗γ∗q∗PQ+kp∗λr∗(1−q)2 in both sides?

This issue is already corrected by The electrician's post...

that being said, multiplying both he numerator and denominator by λb∗γ∗q∗PQ+kp∗λr∗(1−q)2 would only get you a signal denominator for the right side of the equation. you would then have to find a common denominator between the two sides. While this could be done by hand, it would be tedious. It would be easier to do it as seen in the electrician's post.

 

[wel]

I'm not familiar with Maple, but in Mathematica there are two commands useful for this sort of thing.

Apart[] performs a partial fraction decomposition.

Together[] combines terms into a single fraction.

Maple no doubt has similar commands.

Here's what I get by combining terms:

Now you can collect powers in the numerator and denominator to get the form suggested by donpacino.

I don't have Mathematica and not familiar with it. Could you please try with this equation in Mathematic and tell me what you get.
\begin{equation}
[(k_f+k_d+k_p*(1-q))(\lambda_b* \gamma *q*P_Q+k_p*\lambda_r*(1-q)^2)+k_n*\lambda_b*\gamma*q*P_Q]*(\gamma*q*P_Q) - (I*\alpha)(\lambda_b* \gamma *q*P_Q+k_p*\lambda_r*(1-q)^2)(k_p*(1-q)*P_C)=0
\end{equation}

 

[wel]

From the Electrician answer,
His final answer must equal to zero. then the denominator will goes off and i only have to collect the powers in the numerator bit.

 

[The Electrician]

I don't have Mathematica and not familiar with it. Could you please try with this equation in Mathematic and tell me what you get.
\begin{equation}
[(k_f+k_d+k_p*(1-q))(\lambda_b* \gamma *q*P_Q+k_p*\lambda_r*(1-q)^2)+k_n*\lambda_b*\gamma*q*P_Q]*(\gamma*q*P_Q) - (I*\alpha)(\lambda_b* \gamma *q*P_Q+k_p*\lambda_r*(1-q)^2)(k_p*(1-q)*P_C)=0
\end{equation}

Here's what I get if I expand the left side and then collect powers of q:

I notice that in my earlier posts, I used two different symbols Pq and PQ for the same thing. Taking that into account, this result is the same as my previous result for the numerator.

Surely Maple has an "Expand" command.

 

[wel]

Thank you very much the Electrician.