Hi Maryam!
I understand that you are trying to perform mesh decimation only on the part of the green area created by the “patch” function in your code.
I would suggest storing this green patch in an object, let’s say “p”, and then passing “p” to the “reducepatch” function to perform the mesh decimation.
For more information on the “patch” function and how to store and access it as an object, refer to the following documentation page: https://www.mathworks.com/help/matlab/ref/patch.html#d124e1107225:~:text=the%20previous%20syntaxes.-,p%20%3D%20patch(,),-returns%20the%20patch
For more information on the “reducepatch” function, refer to the following documentation page: