Don't just assume that the start time is zero.

[bangerth]

We have code such as this:

const double t = (this->simulator_is_past_initialization()) ? this->get_time() : 0.0;

This code is used because if we're still initializing the simulator, the current time is not yet available. The line above then simply assumes that the current time is zero -- but that's dangerous, because the start time might in fact be something else than zero, as witnessed by

    start_time              = prm.get_double ("Start time");
    if (convert_to_years == true)
      start_time *= year_in_seconds;

The right thing for these places to do is to query this->get_start_time(). That function doesn't exist yet, but I'm going to add that next.

[bangerth]

At least the following two places are affected:

benchmarks/rigid_shear/plugin/rigid_shear.cc:129:          const double t = (this->simulator_is_past_initialization()) ? this->get_time() : 0.0;
benchmarks/rigid_shear/plugin/rigid_shear.cc:223:          const double t = (this->simulator_is_past_initialization()) ? this->get_time() : 0.0;