rect solver is still used by default, but now
<code>samc-class</code> objects can now be switched between the direct
solver and an iterative solver. In general, the direct solver should be
used where possible, and the iterative solver should be used when the
problem cannot be solved within the memory constraints of the system.
The iterative solver in samc runs until the error of the result is
within the tolerance of the machine precision; in other words the
iterative solver should have 15-16 digits of preci