This flag enables an optimization for the `HEAT_CONDUCTION`

process:

the linear solver will only do the `compute()`

^{*} step if the time step size changes.

This flag is a further optimization on top of the <linear> flag. Thus, the requirements of `<linear>`

apply to this flag, too!

- Attention
- This is an expert option. It comes with a number of further
**requirements above those of **`<linear>`

. These are:

- The linear solver used to solve the process equations must be exclusively used for a single process (or for a single
`process_id`

in the case of staggered coupling). Otherwise the equation system the linear solver has to solve would not only change upon time step size change, but also when switching processes.
- Both, the process equations and the contributions from source terms and boundary conditions must be
**solution and time independent**! In particular, the matrices presented to the linear solver must only change upon time step size change. Note that some boundary conditions (Robin, Python, ...) might contribute not only to the right-hand side of the equation system, but also to the matrix. The contributions to the matrix must be solution and time independent! Also, switching Dirichlet BCs on and off for certain d.o.f.s (e.g., via Python boundary conditions) is not possible!

- Attention
- OGS does not detect whether any or all of the above conditions are met. It is the sole responsibility of the user to ensure the correct usage of this expert option! The user is
**strongly advised to check the correct use of this option** by comparing results to simulation runs that do not use this option!

^{*}: `compute()`

computes the LU decomposition for a direct linear solver, or computes the preconditioner for an iterative linear solver.

#
Additional info

##
From ProcessLib/HeatConduction/CreateHeatConductionProcess.cpp line 88

- This is an optional parameter.
- This parameter has a default value of
`false`

.
- Expanded tag path: processes.process.HEAT_CONDUCTION.linear_solver_compute_only_upon_timestep_change
- Go to source code: → ogs/ogs/master

#
Used in the following test data files

Used in no end-to-end test cases.