COMSOL Multiphysics™

TABLE 2-7: SOLVER ERROR MESSAGES IN LOG WINDOW
SOLVER ERROR MESSAGE
Inf or NaN found, even
when using the minimum
damping factor
Inverted mesh element
near coordinates (x, y, z)
Last time step is not
converged.
Matrix is singular
Maximum number of
linear iterations reached
EXPLANATION
Despite reducing the step size to the minimum value
allowed, the solver cannot evaluate the residual or
modified Newton direction at the new solution iterate.
This essentially means that the current approximation to
the solution is close to the boundary of the domain where
the equations are well-defined. Check the equations for
divisions by zero, powers, and other functions that can
become undefined for certain inputs.
In some mesh element near the given coordinates, the
(curved) mesh element is (partially) warped inside-out.
More precisely, the Jacobian matrix for the mapping from
local to global coordinates has a negative determinant at
some point. A possible reason is that the linear mesh
contains a tetrahedron whose vertices all lie on a
boundary. When improving the approximation of the
boundary using curved mesh elements, the curved mesh
element becomes inverted. To see whether this is the case,
you can change Geometry shape order to 1 in the Model
Settings dialog box, which means that curved mesh
elements will not be used. You can usually avoid such bad
tetrahedra by using a finer mesh around the relevant
boundary. Another reason for this error message can be
that the mesh becomes inverted when using a deformed
mesh.
The last time step returned from the time-dependent
solver is not to be trusted. Earlier time steps are within the
specified tolerances.
When encountered during time-dependent solution: the
linear system matrix (which is a linear combination of the
mass-, stiffness-, and possibly, damping-matrices) is singular.
Usually the problem originates from the algebraic part of a
DAE. In particular, the cause can often be found in weak
constraints or constraint-like equations like the continuity
equation in incompressible flow.
The iterative linear system solver failed to compute a
Newton direction in the specified maximum number of
iterations.
422 | CHAPTER 2: DIAGNOSTICS