multilayer SW solver requires dgesv

[rjleveque]

Running nose tests on a new AWS EC2 instance revealed this issue in rpn2_layered_shallow_water.f90

lapack is required or at least the subroutine dgesv and any dependencies:

riemann/src/rpn2_layered_shallow_water.f90

Line 103 in 3d89c52

external dgesv

[mandli]

Are you thinking we should fall-back to directly compiled source for the routine? We definitely do not want to usually do this.

[rjleveque]

Yes, best to use lapack if available. But we could provide something like we do for this example:
https://github.com/clawpack/apps/blob/master/fvmbook/chap17/advdiff/tridiag.f

[mandli]

So we would need to come up with some sort of check to see if we can link against a native LAPACK. Obviously a configure could do this so we probably need to come up with something similar.

[rjleveque]

Or should we just cleanly skip this unit test if lapack isn't available, as happens with the netCDF tests?

[mandli]

Might be easiest.