trestarting.rst - pism - [fork] customized build of PISM, the parallel ice sheet model (tillflux branch)
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       trestarting.rst (2692B)
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            1 .. include:: ../../global.txt
            2 
            3 Initialization from a saved model state
            4 ---------------------------------------
            5 
            6 "Initialization" has the specific, simple meaning in PISM that option ":opt:`-i`" was
            7 used. If a previous PISM run has saved a NetCDF file using ":opt:`-o`" then that file will
            8 contain complete initial conditions for continuing the run. The output file from the last
            9 run can be loaded with ":opt:`-i`":
           10 
           11 .. code-block:: none
           12 
           13    pisms -eisII A -y 100 -o foo.nc
           14    pisms -eisII A -i foo.nc -y 100 -o bar.nc
           15 
           16 As noted verification tests (section :ref:`sec-verif`) and simplified-geometry experiments
           17 (section :ref:`sec-simp`) do not need input files at all because they initialize from
           18 formulas in the source code. They can, however, be continued from saved model states using
           19 :opt:`-i`. Specifying the simplified geometry experiment or verification test *is*,
           20 however, necessary if the run is to continue with the climate inputs for that experiment
           21 or test. For example, based on the above ``pisms`` runs, it is valid to do
           22 
           23 .. code-block:: none
           24 
           25    pismr -i foo.nc -y 100 -o bar.nc
           26 
           27 but the climate and other parameters use PISM default values, and thus are not
           28 (necessarily) the values specified in EISMINT II.
           29 
           30 As a technical note about saved states, a PISM run with :opt:`-stress_balance ssa` also
           31 saves the last SSA velocities to the output file in variables :var:`u_ssa` and
           32 :var:`v_ssa`. The presence of these velocities adds efficiency in restarting because an
           33 initial estimate speeds up the solution of the SSA stress balance equations. If you want
           34 to use :opt:`-i` but also ignore these velocities then set
           35 :config:`stress_balance.ssa.read_initial_guess` to *false*.
           36 
           37 .. _sec-i-format:
           38 
           39 ``-i`` file format
           40 ^^^^^^^^^^^^^^^^^^
           41 
           42 PISM produces CF-1.5 compliant NetCDF files. The easiest way to learn the output format
           43 *and* the :opt:`-i` format is to do a simple run and then look at the metadata in the
           44 resulting file, like this:
           45 
           46 .. code-block:: none
           47 
           48    pisms -eisII A -y 10 -o foo.nc
           49    ncdump -h foo.nc | less
           50 
           51 Note that variables in the output file have a ``pism_intent`` attribute. When
           52 ``pism_intent`` is ``diagnostic``, the variable can be deleted from the file without
           53 affecting whether PISM can use it as a :opt:`-i` input file. Variables with
           54 ``pism_intent`` is ``model_state``, by contrast, must be present when using :opt:`-i`.
           55 
           56 The automatically-produced :var:`time` variable has a ``units`` attribute like ``"seconds
           57 since 1-1-1"`` because the CF metadata conventions require a reference date.
           58 
           59 .. FIXME: double-check the statement below
           60 
           61 By default PISM ignores this reference date except when it is used in unit conversions
           62 based on a calendar (see below).