COMSOL Multiphysics™

femtime
initial values are consistent (seldom the case since the initial value of the time
derivative is 0). Otherwise, the solver tries to modify the initial values so that they
become consistent. The value Consistent=on can be used for index-1 DAEs. Then
the solver fixes the values of the differential DOFs, and solve for the initial values of
the algebraic DOFs and the time derivative of the differential DOFs. The value
Consistent=bweuler can be used for both index-1 and index-2 DAEs. Then the
solver perturbs the initial values of all DOFs by taking a backward Euler step.
For a DAE system, if Estrat=1, then the algebraic DOFs are excluded from the
error norm of the time discretization error.
You can suggest a size of the initial time step using the property Initialstep.
By default, the solver determines whether the system is differential-algebraic by
looking after zero rows or columns in the mass matrix. If you have a DAE where the
mass matrix has no zero rows or columns, put Masssingular=yes.
The property Maxorder gives the maximum degree of the interpolating polynomial
in the BDF method.
The property Maxstep puts an upper limit on the time step size.
The property Out determines the output arguments and their order. The solution
object fem.sol contains the output times and the corresponding solutions, see
femsol. By default, the time derivatives are not stored in the solution. To store
them, use the Outcomp property, see femsolver. This will also give a more accurate
value in postprocessing of values interpolated in time. The output u is a matrix
whose columns are the solution vectors for the output times. The output tlist is
a row vector containing the output times. The output variable Stop is 0 if a
complete solution was returned, 1 if a partial solution was returned, and 2 if no
solution was returned. For the other outputs, see femlin.
The property Stop makes it possible to return a partial solution when the time
stepping fails at some point. If a failure occurs, the computed time steps are returned
in sol.
Use the property Stopcond to make sure the solver stops before a certain event. You
provide a scalar expression that is evaluated after each time step. The time stepping
is stopped if the real part of the expression is evaluated to something negative. The
corresponding solution, for which the expression is negative is not returned.
You can use the property Keep to tell femtime that certain quantities are constant
in time, which sometimes can speed up the computation, see “Manual Control of
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