There are several issues.
- k(1,t) < 10 returns a vector, not a scalar
- Similarly, Ca(t) is a vector.
- It looks like you really want to loop through all the elements and if that's the case, you need to deal with one t a time
- If above is true, you probably want to use && instead of &
- Based on all above, you can see that your current script is only executed once and it lands in the last condition.
- Finally, you may want to consider vectorizing the code using logical index and in that case you do want to use &, not &&. As an example:
Ca = 40*ones(size(t));
Ca(k(1,t)<10 & k(1,t)>1) = 10;
