ODE45 error message "Error using exist The first input to exist must be a string scalar or character vector"

Below is my code to solve a population balance:

global param w0 w

param0=[1 1 1 1] 
param=param0

param=fminsearch(lau,param0)

psi_lau=param(1)
alfa_lau=param(2)
beta_lau=param(3)
epsilon_lau=param(4)



function sse=lau(param)

global param w0 w t
w0=[0.1 0.2 0.23 0.4 0.2 0.1 0.1 0.01];
w=w0
t0=[0 0 0 0 0 0 0 0];
tp=[5 5 5 5 5 5 5 5];
t=t0

[t,w]=ode45(grinding,[t0 tp],w0)
wdata=  [1 1 1 1 1 1 1 1 ; % weight fraction pada t=60
         1 1 1 1 1 1 1 1 ; % weight fraction pada t=120
         1 1 1 1 1 1 1 1 ; % weight fraction pada t=180
         1 1 1 1 1 1 1 1 ; % weight fraction pada t=240
         1 1 1 1 1 1 1 1 ]; % weight fraction pada t=300

%w= (2*param(1)^2).*wdata; % weight fraction hasil simulasi

sse=sum(sum((wdata-w).^2)'); % sums of square error

end


function dwdt=grinding(t,w)

global param w0 w

x=[0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2];
w
param

for k=1:length(x)
       
    S(k)=(param(2)*x(k)^param(3))/(1+x(k)^param(4));
    
    for u=2:k
        
        deltaB(k,u)=((x(k-1))/x(u))^param(1)-((x(k)/x(u))^param(1));
            
    end

end



for k=1:length(x)
   
WS(k)=w(k).*S(k);


end
S
deltaB
summation=WS*deltaB

for k=1:length(x)
dwdt(k)=summation(k)-S(k)*w(k);

end
dwdt

end

It trigger an error of

Error using exist
The first input to exist must be a string scalar or character vector.

Error in odearguments (line 59)
  if (exist(ode)==2)

Error in ode45 (line 115)
    odearguments(FcnHandlesUsed, solver_name, ode, tspan, y0, options, varargin);

Error in Optimize>lau (line 26)
[t,w]=ode45(grinding,[t0 tp],w0)

Error in Optimize (line 8)
param=fminsearch(lau,param0)

Could anybody help to solve the issue, sorry to put a lot of tracker for debuging purpose, thanks

Answer 1

[Torsten]

param = fminsearch(@lau,param0)

[t,w] = ode45(@grinding,[t0 tp],w0)

[Khanif Eko Prasetyo]

Thanks alot, it's solve for the ode thing