Using a custom solver version

Setting the solver path

CasADi searches its own installation directory before CASADIPATH, so CASADIPATH alone cannot reliably override a bundled solver. RTCTOOLS_EXTRA_CASADIPATH is used instead — it is prepended to CasADi’s search path before the solver is instantiated, giving it the highest priority.

RTCTOOLS_EXTRA_CASADIPATH is read by run_optimization_problem() and run_simulation_problem(). If you instantiate a problem class directly, configure the path yourself before solving using casadi.GlobalOptions.getCasadiPath() and casadi.GlobalOptions.setCasadiPath() — read the current path first and prepend to it, rather than replacing it outright, to preserve the CasADi install directory.

When the path is set, RTC-Tools logs the active CasADi plugin search path at INFO level so you can confirm the override is in effect.

# Linux/macOS
export RTCTOOLS_EXTRA_CASADIPATH="/path/to/custom/solver/lib"

# Windows
set RTCTOOLS_EXTRA_CASADIPATH=C:\path\to\custom\solver\lib

Windows only: the solver library (e.g. libhighs.dll) is a transitive dependency of the plugin wrapper and is resolved by the standard Windows DLL search order (PATH). Set PATH to include the custom solver directory before starting the Python process so that the correct version is found rather than any copy already present on the system:

set PATH=C:\path\to\custom\solver\lib;%PATH%
set RTCTOOLS_EXTRA_CASADIPATH=C:\path\to\custom\solver\lib

Custom solver folder contents

The directory must contain the solver library and the CasADi plugin wrapper. For HiGHS as an example:

Linux	Windows	Role
`libhighs.so`	`libhighs.dll`	Solver library
`libcasadi_conic_highs.so`	`libcasadi_conic_highs.dll`	CasADi plugin wrapper

The plugin wrapper is compiled against both the CasADi source (for internal headers) and the HiGHS headers. The solver library must match the HiGHS version the wrapper was compiled against — the headers encode vtable layouts and struct sizes that must match exactly. Using mismatched versions causes silent data corruption or crashes at runtime. The bundled CasADi wrapper cannot be reused for a different HiGHS version — always build a new one.

Note

If the plugin directory exists but the wrapper fails to load (e.g. ABI mismatch or a missing transitive DLL on Windows), CasADi reports the error when the solver is instantiated, not when the path is configured. Check the CasADi error output in that case.