First a suggestion, this line really doesn't make any sense:
just do
and you get the same result and you don't have to carry around extra syntax. Still i'm not sure that you wanted M as a double since you use it as an array later.
Then the error is on line:
Kn = K1*M(t)*M(1)-K1*M(1)*M(t)-mui*M(t);
You are trying to access a double (M) as if it was an array with M(t). M has only one element and using an index on it doesn't really work. What's more is that the index that you are using later, dt, is not an integer, meaning that it cannot be resolved anyways. What's the element 0.1 in an array? Positions only go by integers, so 1,2,3,...
Later in the code at line:
K(i+1) = K(i)*M1(i)*Mn(i)-K(i)*M1(i)*Mn(i)-mui(i)*Mn(i) ;
you use a variable that doesn't exist, M1. This will throw an error as well
I would suggest a solution but i'm very confused by what we are trying to achieve.
Also if you could write the equation in LateX it would be better.
