Real solution for a variable in an equation
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Hi all, I have an equation and I want to find the real solution (c>0), for eqn, but this code doesn't work. Could you please tell me what is wrong in the below code that I wrote. Thanks in advance for any help
V_plc=0.19;
Kf=0.18;
Kc=0.1;
Kp=0.15;
Kb=0.4;
Kh=0.05;
tau=0.18;
Ktau=0.045;
Vs=0.002;
Kbar=1.5e-5;
Ks=0.1;
Vpm=1.59e-4;
Kpm=0.15;
alpha0=6.81e-6;
alpha1=2.27e-5;
Kce=7;
delta=0.1;
gamma=5.5;
Kplc=0.055;
k_i=2;
ct=0.07;
syms c
p=(V_plc.*c.^2/(c.^2+Kplc.^2))./k_i;
h=Kh.^4./(Kh.^4+c.^4);
Po=((p.^2)*(c.^4).*h)./((p.^2).*(c.^4).*h.*(1+Kb)+Kb.*Kp.^2*(Kc.^4+c.^4-((c.^4*Kh.^4)./(c.^4+Kh.^4))));
jpm=Vpm.*(c.^2/(c.^2+Kpm.^2));
eqn=(((alpha1.*Kce.^4)./(jpm-alpha0))-Kce.^4).^(1/4)-((Vs.*c.^2)./(Kf.*Po.*(c.^2+Ks.^2)))-c==0;
S = solve(eqn,c,'Real',true)
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Accepted Answer
Chunru
on 29 Aug 2022
V_plc=0.19;
Kf=0.18;
Kc=0.1;
Kp=0.15;
Kb=0.4;
Kh=0.05;
tau=0.18;
Ktau=0.045;
Vs=0.002;
Kbar=1.5e-5;
Ks=0.1;
Vpm=1.59e-4;
Kpm=0.15;
alpha0=6.81e-6;
alpha1=2.27e-5;
Kce=7;
delta=0.1;
gamma=5.5;
Kplc=0.055;
k_i=2;
ct=0.07;
syms c
p=(V_plc.*c.^2/(c.^2+Kplc.^2))./k_i;
h=Kh.^4./(Kh.^4+c.^4);
Po=((p.^2)*(c.^4).*h)./((p.^2).*(c.^4).*h.*(1+Kb)+Kb.*Kp.^2*(Kc.^4+c.^4-((c.^4*Kh.^4)./(c.^4+Kh.^4))));
jpm=Vpm.*(c.^2/(c.^2+Kpm.^2));
% eqn=(((alpha1.*Kce.^4)./(jpm-alpha0))-Kce.^4).^(1/4)-((Vs.*c.^2)./(Kf.*Po.*(c.^2+Ks.^2)))-c==0;
% S = solve(eqn,c,'Real',true)
% The function you specified is a complex function that has no solution.
% Check out abs(f) which never reaches to 0.
f1= (((alpha1.*Kce.^4)./(jpm-alpha0))-Kce.^4).^(1/4)-((Vs.*c.^2)./(Kf.*Po.*(c.^2+Ks.^2)))-c;
fplot(real(f1), [0 1]); hold on
fplot(imag(f1), [0 1])
fplot(abs(f1), [0 1])
ylim([-1 1]*5)
xlim([0 0.4])
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