checkpoint Module

Checkpoints are Fortran unformatted (stream) binary files that capture everything needed to resume a run exactly:

• A magic integer (42) and version (1) for format identification.
• Scalars: iter, t, n_pt, neq, dt.
• The conserved-variable array ub(neq, n_pt).
• An optional BDF2 previous-step array bdf2_ub_prev(neq, n_pt), preceded by a presence flag (integer 1 = present, 0 = absent).

File naming: <base>_NNNNNN.bin where NNNNNN is the zero-padded iteration number. A companion text file latest_checkpoint (written alongside) records the path of the most recent checkpoint so that restart drivers need not track the iteration themselves.

Typical usage in the driver: @code use checkpoint, only: write_checkpoint, read_checkpoint ! --- writing --- call write_checkpoint(state, cfg%checkpoint_file, t, iter) ! --- reading --- call read_checkpoint(state, cfg%restart_file, t, iter) @endcode

Variables

Type	Visibility	Attributes		Name		Initial
integer,	private,	parameter	::	CKPT_MAGIC	=	42
integer,	private,	parameter	::	CKPT_VERSION	=	1

Functions

private function resolve_latest(fname, is_ok, message) result(actual)

Arguments

Type	Intent	Optional	Attributes		Name
character(len=*),	intent(in)			::	fname
logical,	intent(out),	optional		::	is_ok
character(len=*),	intent(out),	optional		::	message

Return Value character(len=512)

Subroutines

public subroutine write_checkpoint(state, base, t, iter, is_ok, message)

Write a checkpoint file for the current solver state.

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Arguments

Type	Intent	Optional	Attributes		Name
type(solver_state_t),	intent(in)			::	state	Current solver state (must have ub allocated).
character(len=*),	intent(in)			::	base	Base name (e.g. 'checkpoint'); file = base_NNNNNN.bin.
real(kind=wp),	intent(in)			::	t	Current simulation time [s].
integer,	intent(in)			::	iter	Current iteration number.
logical,	intent(out),	optional		::	is_ok
character(len=*),	intent(out),	optional		::	message

public subroutine read_checkpoint(state, fname, t, iter, is_ok, message)

Read a checkpoint file and restore solver state.

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Arguments

Type	Intent	Optional	Attributes		Name
type(solver_state_t),	intent(inout)			::	state	Solver state with ub already allocated (from setup_solver).
character(len=*),	intent(in)			::	fname	Path to the checkpoint file (or 'latest_checkpoint').
real(kind=wp),	intent(out)			::	t	Restored simulation time [s].
integer,	intent(out)			::	iter	Restored iteration count.
logical,	intent(out),	optional		::	is_ok
character(len=*),	intent(out),	optional		::	message

private subroutine update_latest(fname, is_ok, message)

Arguments

Type	Intent	Optional	Attributes		Name
character(len=*),	intent(in)			::	fname
logical,	intent(out),	optional		::	is_ok
character(len=*),	intent(out),	optional		::	message