Update design parameter in TO

Hi. in tutorial 18 of gridap I couldn’t understand how gridap update design density. because i have done similar but it always gives me zero and says that the matrix A is singular. can anyone explain me about the procedure? thank you

Please read

and amend your question accordingly. In this case this would likely mean linking to the tutorial in question and ideally copying out the bits that aren’t working for you in a way that others can run it on their machines (i.e. including importing relevant packages and defining all variables used).