Frequently asked questions

The build stops with cannot find -lcudart.

Your CUDA installation is not where the build is looking. Run make config to see what it found, then make CUDAPATH=/path/to/cuda.

The build stops with Unsupported gpu architecture.

Your CUDA release no longer supports the architecture being requested. Recent releases have dropped older ones. CUDA 13, for instance, no longer accepts sm_61. The gravity library normally detects your card from nvidia-smi, and if that is unavailable or not working you can pass the compute capability yourself with make COMPUTE_CAPABILITY=75 (where “75” is replaced with ten times the compute capability).

I have no NVIDIA card. Can I still use StarSmasher?

Yes. make cpu builds a version that needs no GPU. It is not as slow as you might expect, because the GPU only takes over the gravity. See Running a simulation for measured timings.

The run stops immediately with init: error reading input file sph.init.

A run needs sph.init. It is three lines. See sph.init.

The run stops with Cannot match namelist object name.

sph.input sets a variable that is not in the namelist. Check it against sph.input.

My relaxed star has particles flying off.

Often the particle-mass distribution. For a giant star spanning many orders of magnitude in density, equalmass=0 doesn’t resolve the central regions well, which launches a shock wave outward and the low-mass outer particles never settle. See Relaxing a star.

How many neighbours does nnopt give me?

More than nnopt: the actual count is larger by roughly 1.4 to 1.7 depending on the kernel. nnopt is the target of the smoothing-length constraint, not a neighbour count. See Equations of motion.

Which of parallel_bleeding_edge and Blackollider should I use?

parallel_bleeding_edge unless you are modelling collisions with significantly massive compact objects treated as point masses. The two differ mainly in how the smoothing length is related to the density.

My restarted run isn’t appending to energy0.sph.

It’s not supposed to. Output is numbered per stage: a resumed run writes log1.sph and energy1.sph, for example, rather than appending to the originals.