How to change PDE coefficients in specific nodes?

Hi users,

I am solving a water diffusion problem in a 2D planar domain. I am using a Matlab code, not the PDETool GUI. I have all the PDE coefficients expressed as a function of the time and the script works so well at the moment.

In the next step, I need to add a perturbation in the problem altering one of the PDE coefficients (the 'c' coefficient) in specific nodes of the mesh.

Does MATLAB allow this?

Thanks in advance

MG