Initial conditions should have instructions & be selectable for all variables (repost of SimVascular/svZeroDSolver#141)

Problem

The documentation does not make it clear how to set initial conditions. This is especially unclear for internal state variables such as the Windkessel pressure in an RCR bc or the chamber state variables.

This was originally opened in the svZeroDSolver itself. https://github.com/SimVascular/svZeroDSolver/issues/141#issuecomment-3134532653

Solution

The documentation should show examples of setting initial conditions for state variables. The variable "pressure_c:OUTLET" appears to control the windkessel pressure in the RCR.

An example of initial condition block is:

"initial_condition": {
    "Vc:ventricle": 69.530841853596712,
    "pressure:vessel:OUTLET": 1.333223680000000e+05,
    "pressure:INFLOW:valve0": 0.0,
    "pressure:valve0:ventricle": 0.0,
    "pressure:ventricle:valve1": 0.0,
    "pressure:valve1:vessel": 1.333223680000000e+05,
    "pressure_c:OUTLET": 1.333223680000000e+05
}

Additional context

It is possible that some of these variables are initialized in some hard coded manner, to zero, estimated steady state only, etc. If this is the case, then code to set initial values for all possible variables should be added and it should be mentioned which state variables cannot be changed.

Code of Conduct

• I agree to follow this project's Code of Conduct and Contributing Guidelines

Start with the linked svZeroDSolver issue and the repository's documentation entry points; no specific file or test is named here. Document examples for setting initial conditions, including internal state variables such as Windkessel pressure and chamber states, and clearly identify any variables that cannot be changed.