the following link can help you:

https://www.comsol.com/support/knowledgebase/953

Good luck

You need to check determinant of your matrix, so if it is singular it will never work. Try to check your system of equations, dimensions, and than its determinant must be non zero.... Also check your code and compatibility of your matrices w.r.t binary operations.

I have checked my equations and boundary conditions properly there is no problem. I have one pair of equations where there is no boundary condition but only initial conditions and I am guessing that must be the case.

Dear Afaz Ul Hoq ,

The system matrix (Jacobian matrix or stiffness matrix) is singular, so the solver cannot invert it. Usually this means that the system is underdetermined. Check that all equations are fully specified and that the boundary conditions are appropriate. For instance, in a stationary model you usually need to have a Dirichlet condition on some boundary (that is, specifying the value of the solution on the boundary).

A singular matrix could also occur if mesh elements are of too low quality. If the minimum element quality is less than 0.005 you might be in trouble (to check the mesh quality, plot the built-in variable qual). Another reason for this error message is that you have different element orders for two variables that are coupled by, for example, a weak constraint. Use the same element order for all variables that are coupled,

Best

I have checked the equations and boundary conditions they are fine but the thing is I have 5 PDE to solve where first three are space dependent and last two are time-dependent. So when I am using the stationary study I am getting the correct results for the space-dependent variables but however when I am trying to find the time-dependent variable solution I am getting zero values for those equations.

Now I have all the 5 equations coupled to one another.

I am using comsol 5.4 version if anyone can help me to fix this error and get me a solution I can share my comsol file.

Regards