How can I prevent MATLAB from changing certain initial conditions using ode15s?

I am trying to solve a DAE system using ode15s.

Due to the structure of ode15s I have to input initial conditions for all variables, however using degrees of freedom analysis on the problem only the differential equations need initial conditions. Due to that, I obtained all of the initial conditions in another MATLAB script and input them in ode15s. As MATLAB converges, however, it's changing the initial conditions of the 2 differential equations (which are the only ones that need to remain constant, in order to solve the required physical problem).

Is there a way to ensure that certain initial conditions remain unchanged?

Is there a way to add inequality constraints on the outputs of ode15s?

Thank you.

[Walter Roberson]

Do not solve for them and make them input parameters perhaps?

https://www.mathworks.com/help/matlab/math/parameterizing-functions.html