解微分方程组碰到的问题，求高手赐教！
 

function xdot=mfceq3(t,x)
%S--x(1);xa--x(2);xm--x(3);Mox--x(4)
global F R T Y qmaxa qmaxm umaxa umaxm Ksa Ksm M r Mtotal Mred...
KM Kda Kdm Xmaxa Xmaxm Kx Rext Rint Rmin Rmax Eocv Emin Emax KR ...
S0 V Fin Asur i0ref ebc Imfc ...
S xa xm Mox
xdot=[-qmaxa*x(1)*x(4)*x(2)/((Ksa+x(1))*(KM+x(4)))-qmaxm*x(1)*x(3)/(Ksm+x(1))+Fin*(S0-x(1))/V;

umaxa*x(1)*x(4)*x(2)/((Ksa+x(1))*(KM+x(4)))-...
Kda*x(2)-(1+tanh(Kx*(x(2)+x(3)-Xmaxa)))*Fin*x(2)/(2*V);

umaxm*x(3)*x(1)/(Ksa+x(1))-Kdm*x(3)-(1+tanh(Kx*(x(2)+x(3)-Xmaxm)))*Fin*x(3)/(2*V);

r/(M*F*V*x(2)*(Rext+Rmin+(Rmax-Rmin)*...
exp(-KR*x(2))))*(Emin+(Emax-Emin)*exp(1/(KR*x(2)))-...
(R*T*log(Mtotal/(Mtotal-x(4)))/(M*F)))-Y*qmaxa*x(1)*x(4)/((Ksa+x(1))*(KM+x(4)))];%Rint递减

clc;
clear all;
global F R T Y qmaxa qmaxm umaxa umaxm Ksa Ksm M r Mtotal Mred...
KM Kda Kdm Xmaxa Xmaxm Kx Rext Rint Rmin Rmax Eocv Emin Emax KR ...
S0 V Fin Asur i0ref ebc Imfc ...
S xa xm Mox
F=96485;R=8.314472;T=298.15;Y=22.75;
qmaxa=8.48;qmaxm=8.20;%--**/d
umaxa=1.97;umaxm=0.1;
Ksa=20;Ksm=80;
M=2;r=663400;
Mtotal=0.05;
KM=0.01;%KM=0.2*Mtotal
Kda=0.04;Kdm=0.002;%Kda=0.02*umaxa;Kdm=0.02*umaxm;
Xmaxa=512.5;Xmaxm=525;
Kx=0.04;
Rext=1000;%……
Rmin=25;Rmax=2000;
Emin=0.01;Emax=0.66;
KR=0.006;
S0=1000;%many values
% S0=310;
V=0.05;%--L
Fin=5;
Asur=0.05;%5cm*10cm
i0ref=2e-4;%????
ebc=0.0001;%~0

[t,x]=ode15s('mfceq3',[0 5],[0 265 265 0]);
S=x(:,1);
xa=x(:,2);
xm=x(:,3);
Mox=x(:,4);

Rint=Rmin+(Rmax-Rmin)*exp(KR*xa);
Eocv=Emin+(Emax-Emin)*exp(-1/(KR*xa));
Rint=Rint';

Imfc=(Eocv-(R*T*log10(Mtotal/(Mtotal-Mox))/(M*F)))/(Rext+Rint);
plot（Imfc）


Imfc曲线画不出来，Imfc是个无效数，百思不得其解，请高手赐教，如何可以的话，请加我QQ916878521，谢谢