Rate constant estimation and optimization (ODE)

I am totally new to matlab coding. I have written a code on a simple ODE "dCdt=-k1*CS*CH". I want to find the 'k' value and optimize it such that the error between my experimental and calculated concentration values is low. The code runs, but it accepts all the initial guess 'k' values. How should I find my actual 'k' value.

function SSE=myobjective(C,CS)
err=C-CS;
SSE=sum(err.^2)

k1=.001;
tspan=linspace(1,5,6);
CS0=2;
CH=1;
CS=[1.8 .78 .40 .16 .071 .022]';
[t,C]=ode45(@(t,CS) funcatalyst(t,CS,CH, k1),tspan,CS0)
options=optimset('display','iter','largescale','off','maxiter',10000,'maxfunevals',10000);
[k, fval,exitflag,output]=fminsearch(@(k) myobjective(C,CS), k1, options)

Answer 1

[Alan Weiss]

You might find this example or this example to be relevant.

Alan Weiss

MATLAB mathematical toolbox documentation