This adds a check that the step size is positive, and I've made a small fix to the simulation algorithm that makes it handle the last time step properly so that t never exceeds the end time, even if the step size is greater than the total simulation time.
This adds a check that the step size is positive, and I've made a small fix to the simulation algorithm that makes it handle the last time step properly so that t never exceeds the end time, even if the step size is greater than the total simulation time.
This closes issue #14.