Inconsistencies in brms predictions for spline models

Minimal reproducible example to demonstrate significant inconsistencies sometimes seen in predictions of brms spline models in different environments.

• Run renv::restore() to set up the package environment.
• Minimal example: /scripts/mortality.R, rename output as appropriate.
• Models trained in different environments are located in /models.
• Analysis scripts are located in /scripts.
• Plots of cluster and Ubuntu models in both environments are located in /plots.

Summary of results

Training Environment	R-sq cluster_R4_1_1	R-sq debian_R3_6_3	R-sq macos_R4_1_1	R-sq ubuntu_R4_1_1	R-sq windows_R4_1_1
cluster_R3_6_3	0.99823444	0.99823444	0.48131956	0.48131956	0.48131956
cluster_R4_1_1	0.99823444	0.99823444	0.48131956	0.48131956	0.48131956
cluster_R4_1_3	0.99823444	0.99823444	0.48131956	0.48131956	0.48131956
debian_R3_6_3	0.99823289	0.99823289	0.48123877	0.48123877	0.48123877
macos_R4_1_1	0.48348136	0.48348136	0.99823370	0.99823370	0.99823370
ubuntu_R4_1_1	0.48346169	0.48346169	0.99823124	0.99823124	0.99823124
windows_R4_1_1	0.48343821	0.48343821	0.99823314	0.99823314	0.99823314

BLAS/LAPACK library implementations used in our environments

• Ubuntu uses the R-internal "reference (Fortran) implementation" libRblas.so and libRlapack.so.
  • Appears to be derived from the Netlib implementation (version unknown) with some "tuning".
• Debian uses libopenblasp-r0.3.5.so.
  • An OpenBLAS pthread implementation version 0.3.5 (includes optimised LAPACK, version unknown).
• The cluster uses libsci_gnu_82_mp.so.5.0 from module cray-libsci/20.09.1
  • Appears from Module help to be Netlib LAPACK 3.6.1, BLAS version unknown.
• Windows and macOS use the R-internal implementations libRblas.so and libRlapack.so.