matlab - How to fix the variables not moving when doing optimization? -

suppose have function has, 5 inputs: f(z,t1,t2,t3,t4). want optimization using lsqnolin, i.e. min f(z,t1,t2,t3,t4). however, have following request:

user can determine variables t1,t2,t3,t4 optimized. when user input 3 program, means need fix t4 while z,t1,t2,t3 can changed minimum value. if user input 2 program, means need fix t3,t4 while z,t1,t2 can changed minimum value.

i understand can use conditional statement, in program, function can have 20 inputs or more. what's more, program accept input [z,t1,t2,t3,t4] @ same time. find online require optimization of variables [z,t1,t2,t3,t4] @ same time, not particular variable fixed.