  We develop a "semi-parallel" simulation technique suggested by Pretorius and
Lehner, in which the simulation spacetime volume is divided into a large number
of small 4-volumes which have only initial and final surfaces. Thus there is no
two-way communication between processors, and the 4-volumes can be simulated
independently without the use of MPI. This technique allows us to simulate much
larger volumes than we otherwise could, because we are not limited by total
memory size. No processor time is lost waiting for other processors. We compare
a cosmic string simulation we developed using the semi-parallel technique with
our previous MPI-based code for several test cases and find a factor of 2.6
improvement in the total amount of processor time required to accomplish the
same job for strings evolving in the matter-dominated era.
