MATLAB: Ode45 error problem in following code

I'm receiving errors for the following code:

mumax = 0.20;

Ks = 2;

Yxs = 0.58;

Ypx = 0.2;

Sf = 0.37;

Kp= 97.9;

mu = @(S,P) mumax*S./(Ks + S)*(1 – (P/Kp))^0.5; % Monod Equation

rg = @(X,S) mu(S)*X; % Rate of cell growth

rp = @(X,S) Ypx*rg(X,S); % Rate of product formation

F = @(t) 0.05;

dXV = @(t, x) x(4) *rg(x(1), x(2));

dPV = @(t, x) x(4) *rp(x(1), x(2));

dSV = @(t,x) F(t)*Sf – x(4)*rg(x(1), x(2))/Yxs;

dV = @(t,x) F(t);

dX = @(t,x) (dXV(t,x) – x(1)*dV(t,x))/x(4);

dS = @(t,x) (dSV(t,x) – x(2)*dV(t,x))/x(4);

dP = @(t,x) (dPV(t,x) – x(3)*dV(t,x))/x(4);

f = @(t,x) [dX(t,x); dS(t,x); dP(t,x); dV(t,x)];

tspan = [0 100];

[t,x] = ode45(f,tspan,ic);

The error I receive is:

Not enough input arguments.

Error in @(S,P)mumax*S./(Ks+S)*(1-(P/Kp))^0.5

Error in @(X,S)mu(S)*X

Error in @(t,x)x(4)*rg(x(1),x(2))

Error in @(t,x)(dXV(t,x)-x(1)*dV(t,x))/x(4)

Error in @(t,x)[dX(t,x);dS(t,x);dP(t,x);dV(t,x)]

Error in odearguments (line 90)

f0 = feval(ode,t0,y0,args{:}); % ODE15I sets args{1} to yp0.

Error in ode45 (line 115)

odearguments(FcnHandlesUsed, solver_name, ode, tspan, y0, options, varargin);