[deveshvaidyaofficial]

Summary

Currently when dims() processes a std::vector with element type Eigen vector, the existing recursive implementation appends both the row and column dimensions of the Eigen vector . This introduces an extra dimension of size 1 for vector-valued elements.

This change uses is_eigen_vector<T>::value to detect Eigen vector element types and appends their size directly. For other element types, the existing recursive behavior is preserved.Hence it closes #3273

Tests

1. Added dims_nested_vector_arrays to test/unit/math/prim/fun/dims_test.cpp.
2. Tested nested vector containers of Eigen column vectors with dimensions 1 × 1 × 1 and 2 × 3 × 5.
3. Ran python .\runTests.py test/unit/math/prim/fun/dims_test.cpp; both tests passed.

Reproduced the original Stan model using the modified dims.hpp. for testing my fix . The model printed dims(x): [1,1,1], as expected.

Side Effects

None

Release notes

Fix extra dimension error reported by dims() for nested containers of Eigen vectors.

Checklist

• Copyright holder: Devesh Vaidya
  - Code: BSD 3-clause (https://opensource.org/licenses/BSD-3-Clause)
  - Documentation: CC-BY 4.0 (https://creativecommons.org/licenses/by/4.0/)

• the basic tests are passing

  • unit tests pass (to run, use: ./runTests.py test/unit)
  • header checks pass, (make test-headers)
  • dependencies checks pass, (make test-math-dependencies)
  • docs build, (make doxygen)
  • code passes the built in C++ standards checks (make cpplint)

• the code is written in idiomatic C++ and changes are documented in the doxygen

• the new changes are tested

[WardBrian]

Thanks. I think this is probably the correct thing to do, though the old behavior has been around for so long that I am worried about it breaking things

[deveshvaidyaofficial]

I reproduced the MathFunctions.append_array_rev Eigen assertion locally on both my PR branch and a clean worktree of origin/develop. The baseline fails with the same assertion, while MathFunctions.append_array_prim passes. This suggests the failure is pre-existing relative to the baseline tested, rather than caused by the dims() change. I’ll keep the PR focused on the dims() fix and investigate any other CI failures separately. Any suggested fixes?

[stan-buildbot]

Name	Old Result	New Result	Ratio	Performance change( 1 - new / old )
stat_comp_benchmarks/benchmarks/gp_regr/gen_gp_data.stan	0.04	0.04	1.01	1.15% faster
stat_comp_benchmarks/benchmarks/gp_regr/gp_regr.stan	0.17	0.16	1.01	1.15% faster
stat_comp_benchmarks/benchmarks/garch/garch.stan	0.86	0.87	1.0	-0.31% slower
stat_comp_benchmarks/benchmarks/low_dim_corr_gauss/low_dim_corr_gauss.stan	0.01	0.01	0.93	-7.81% slower
stat_comp_benchmarks/benchmarks/eight_schools/eight_schools.stan	0.11	0.11	0.99	-1.3% slower
stat_comp_benchmarks/benchmarks/low_dim_gauss_mix/low_dim_gauss_mix.stan	8.17	8.18	1.0	-0.04% slower
stat_comp_benchmarks/benchmarks/gp_pois_regr/gp_pois_regr.stan	3.68	3.65	1.01	0.75% faster
stat_comp_benchmarks/benchmarks/pkpd/one_comp_mm_elim_abs.stan	32.75	32.79	1.0	-0.12% slower
stat_comp_benchmarks/benchmarks/pkpd/sim_one_comp_mm_elim_abs.stan	0.38	0.38	1.0	0.25% faster
stat_comp_benchmarks/benchmarks/irt_2pl/irt_2pl.stan	6.84	6.81	1.0	0.49% faster
stat_comp_benchmarks/benchmarks/sir/sir.stan	167.26	174.58	0.96	-4.37% slower
stat_comp_benchmarks/benchmarks/arK/arK.stan	3.22	3.21	1.0	0.2% faster
stat_comp_benchmarks/benchmarks/arma/arma.stan	0.61	0.6	1.01	0.68% faster
stat_comp_benchmarks/benchmarks/low_dim_gauss_mix_collapse/low_dim_gauss_mix_collapse.stan	25.87	25.89	1.0	-0.09% slower
performance.compilation	388.15	350.24	1.11	9.77% faster
Mean result: 1.001500311178087

Jenkins Console Log
Jenkins Build Stages
Commit hash: f650e7d0b68a35569be5874169d8951cbf1b6ea6

Machine information

Distributor ID:	Ubuntu
Description:	Ubuntu 20.04.3 LTS
Release:	20.04
Codename:	focal

CPU:

Architecture:                            x86_64
CPU op-mode(s):                          32-bit, 64-bit
Byte Order:                              Little Endian
Address sizes:                           52 bits physical, 57 bits virtual
CPU(s):                                  192
On-line CPU(s) list:                     0-191
Thread(s) per core:                      2
Core(s) per socket:                      48
Socket(s):                               2
NUMA node(s):                            2
Vendor ID:                               AuthenticAMD
CPU family:                              25
Model:                                   17
Model name:                              AMD EPYC 9474F 48-Core Processor
Stepping:                                1
Frequency boost:                         enabled
CPU MHz:                                 1497.701
CPU max MHz:                             4114.4229
CPU min MHz:                             1500.0000
BogoMIPS:                                7189.39
Virtualization:                          AMD-V
L1d cache:                               3 MiB
L1i cache:                               3 MiB
L2 cache:                                96 MiB
L3 cache:                                512 MiB
NUMA node0 CPU(s):                       0-47,96-143
NUMA node1 CPU(s):                       48-95,144-191
Vulnerability Gather data sampling:      Not affected
Vulnerability Indirect target selection: Not affected
Vulnerability Itlb multihit:             Not affected
Vulnerability L1tf:                      Not affected
Vulnerability Mds:                       Not affected
Vulnerability Meltdown:                  Not affected
Vulnerability Mmio stale data:           Not affected
Vulnerability Old microcode:             Not affected
Vulnerability Reg file data sampling:    Not affected
Vulnerability Retbleed:                  Not affected
Vulnerability Spec rstack overflow:      Mitigation; Safe RET
Vulnerability Spec store bypass:         Mitigation; Speculative Store Bypass disabled via prctl
Vulnerability Spectre v1:                Mitigation; usercopy/swapgs barriers and __user pointer sanitization
Vulnerability Spectre v2:                Mitigation; Enhanced / Automatic IBRS; IBPB conditional; STIBP always-on; PBRSB-eIBRS Not affected; BHI Not affected
Vulnerability Srbds:                     Not affected
Vulnerability Tsa:                       Mitigation; Clear CPU buffers
Vulnerability Tsx async abort:           Not affected
Vulnerability Vmscape:                   Mitigation; IBPB before exit to userspace
Flags:                                   fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt pdpe1gb rdtscp lm constant_tsc rep_good amd_lbr_v2 nopl xtopology nonstop_tsc cpuid extd_apicid aperfmperf rapl pni pclmulqdq monitor ssse3 fma cx16 pcid sse4_1 sse4_2 x2apic movbe popcnt aes xsave avx f16c rdrand lahf_lm cmp_legacy svm extapic cr8_legacy abm sse4a misalignsse 3dnowprefetch osvw ibs skinit wdt tce topoext perfctr_core perfctr_nb bpext perfctr_llc mwaitx cpb cat_l3 cdp_l3 hw_pstate ssbd mba perfmon_v2 ibrs ibpb stibp ibrs_enhanced vmmcall fsgsbase bmi1 avx2 smep bmi2 erms invpcid cqm rdt_a avx512f avx512dq rdseed adx smap avx512ifma clflushopt clwb avx512cd sha_ni avx512bw avx512vl xsaveopt xsavec xgetbv1 xsaves cqm_llc cqm_occup_llc cqm_mbm_total cqm_mbm_local user_shstk avx512_bf16 clzero irperf xsaveerptr rdpru wbnoinvd amd_ppin cppc arat npt lbrv svm_lock nrip_save tsc_scale vmcb_clean flushbyasid decodeassists pausefilter pfthreshold avic v_vmsave_vmload vgif x2avic v_spec_ctrl vnmi avx512vbmi umip pku ospke avx512_vbmi2 gfni vaes vpclmulqdq avx512_vnni avx512_bitalg avx512_vpopcntdq la57 rdpid overflow_recov succor smca fsrm flush_l1d debug_swap

G++:

g++ (Ubuntu 9.4.0-1ubuntu1~20.04) 9.4.0
Copyright (C) 2019 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Clang:

clang version 10.0.0-4ubuntu1 
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin

[SteveBronder]

So my issue here is that instead of column/row vectors returning (1, N) or (N, 1) now they are going to return N. So a breaking case here is someone who is using this in a function accepting an array of matrices as an input and using dims to determine if they were working with an array of row or column vectors. I agree with @spinkney that is unintuitive behavior, but I also worry about breaking user space code. I'll try to search on github for stan programs that call dims to see their behavior. I would not be surprised if people assume the opposite behavior of how this function currently works!

[spinkney]

So my issue here is that instead of column/row vectors returning (1, N) or (N, 1) now they are going to return N. So a breaking case here is someone who is using this in a function accepting an array of matrices as an input and using dims to determine if they were working with an array of row or column vectors. I agree with @spinkney that is unintuitive behavior, but I also worry about breaking user space code. I'll try to search on github for stan programs that call dims to see their behavior. I would not be surprised if people assume the opposite behavior of how this function currently works!

We could just document this behavior and keep the code as is.

[stan-buildbot]

Name	Old Result	New Result	Ratio	Performance change( 1 - new / old )
stat_comp_benchmarks/benchmarks/low_dim_gauss_mix_collapse/low_dim_gauss_mix_collapse.stan	8.37	8.14	1.03	2.75% faster
stat_comp_benchmarks/benchmarks/gp_pois_regr/gp_pois_regr.stan	2.17	2.11	1.03	2.63% faster
stat_comp_benchmarks/benchmarks/eight_schools/eight_schools.stan	0.06	0.06	1.01	1.42% faster
stat_comp_benchmarks/benchmarks/irt_2pl/irt_2pl.stan	4.26	4.17	1.02	2.13% faster
stat_comp_benchmarks/benchmarks/garch/garch.stan	0.43	0.42	1.03	2.92% faster
stat_comp_benchmarks/benchmarks/low_dim_gauss_mix/low_dim_gauss_mix.stan	2.68	2.61	1.03	2.8% faster
stat_comp_benchmarks/benchmarks/pkpd/sim_one_comp_mm_elim_abs.stan	0.25	0.24	1.03	2.61% faster
stat_comp_benchmarks/benchmarks/pkpd/one_comp_mm_elim_abs.stan	19.32	18.88	1.02	2.31% faster
stat_comp_benchmarks/benchmarks/gp_regr/gen_gp_data.stan	0.02	0.02	0.99	-1.08% slower
stat_comp_benchmarks/benchmarks/gp_regr/gp_regr.stan	0.1	0.1	1.04	3.84% faster
stat_comp_benchmarks/benchmarks/sir/sir.stan	90.65	87.72	1.03	3.24% faster
stat_comp_benchmarks/benchmarks/arK/arK.stan	1.58	1.54	1.02	2.21% faster
stat_comp_benchmarks/benchmarks/low_dim_corr_gauss/low_dim_corr_gauss.stan	0.01	0.01	0.95	-5.02% slower
stat_comp_benchmarks/benchmarks/arma/arma.stan	0.28	0.28	1.01	0.72% faster
performance.compilation	245.76	238.38	1.03	3.01% faster
Mean result: 1.018430830099542

Jenkins Console Log
Jenkins Build Stages
Commit hash: 03b75dafe4013f7215ee8565c33343a189913c3e

Machine information

Distributor ID:	Ubuntu
Description:	Ubuntu 20.04.3 LTS
Release:	20.04
Codename:	focal

CPU:

Architecture:                            x86_64
CPU op-mode(s):                          32-bit, 64-bit
Byte Order:                              Little Endian
Address sizes:                           46 bits physical, 48 bits virtual
CPU(s):                                  80
On-line CPU(s) list:                     0-79
Thread(s) per core:                      2
Core(s) per socket:                      20
Socket(s):                               2
NUMA node(s):                            2
Vendor ID:                               GenuineIntel
CPU family:                              6
Model:                                   85
Model name:                              Intel(R) Xeon(R) Gold 6248 CPU @ 2.50GHz
Stepping:                                7
CPU MHz:                                 1000.000
CPU max MHz:                             3900.0000
CPU min MHz:                             1000.0000
BogoMIPS:                                5000.00
Virtualization:                          VT-x
L1d cache:                               1.3 MiB
L1i cache:                               1.3 MiB
L2 cache:                                40 MiB
L3 cache:                                55 MiB
NUMA node0 CPU(s):                       0,2,4,6,8,10,12,14,16,18,20,22,24,26,28,30,32,34,36,38,40,42,44,46,48,50,52,54,56,58,60,62,64,66,68,70,72,74,76,78
NUMA node1 CPU(s):                       1,3,5,7,9,11,13,15,17,19,21,23,25,27,29,31,33,35,37,39,41,43,45,47,49,51,53,55,57,59,61,63,65,67,69,71,73,75,77,79
Vulnerability Gather data sampling:      Mitigation; Microcode
Vulnerability Indirect target selection: Mitigation; Aligned branch/return thunks
Vulnerability Itlb multihit:             KVM: Mitigation: Split huge pages
Vulnerability L1tf:                      Not affected
Vulnerability Mds:                       Not affected
Vulnerability Meltdown:                  Not affected
Vulnerability Mmio stale data:           Mitigation; Clear CPU buffers; SMT vulnerable
Vulnerability Old microcode:             Not affected
Vulnerability Reg file data sampling:    Not affected
Vulnerability Retbleed:                  Mitigation; Enhanced IBRS
Vulnerability Spec rstack overflow:      Not affected
Vulnerability Spec store bypass:         Mitigation; Speculative Store Bypass disabled via prctl
Vulnerability Spectre v1:                Mitigation; usercopy/swapgs barriers and __user pointer sanitization
Vulnerability Spectre v2:                Mitigation; Enhanced / Automatic IBRS; IBPB conditional; PBRSB-eIBRS SW sequence; BHI SW loop, KVM SW loop
Vulnerability Srbds:                     Not affected
Vulnerability Tsa:                       Not affected
Vulnerability Tsx async abort:           Mitigation; TSX disabled
Vulnerability Vmscape:                   Mitigation; IBPB before exit to userspace
Flags:                                   fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc art arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc cpuid aperfmperf pni pclmulqdq dtes64 monitor ds_cpl vmx smx est tm2 ssse3 sdbg fma cx16 xtpr pdcm pcid dca sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand lahf_lm abm 3dnowprefetch cpuid_fault epb cat_l3 cdp_l3 intel_ppin ssbd mba ibrs ibpb stibp ibrs_enhanced tpr_shadow flexpriority ept vpid ept_ad fsgsbase tsc_adjust bmi1 avx2 smep bmi2 erms invpcid cqm mpx rdt_a avx512f avx512dq rdseed adx smap clflushopt clwb intel_pt avx512cd avx512bw avx512vl xsaveopt xsavec xgetbv1 xsaves cqm_llc cqm_occup_llc cqm_mbm_total cqm_mbm_local dtherm ida arat pln pts hwp hwp_act_window hwp_epp hwp_pkg_req vnmi pku ospke avx512_vnni md_clear flush_l1d arch_capabilities

G++:

g++ (Ubuntu 9.4.0-1ubuntu1~20.04) 9.4.0
Copyright (C) 2019 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Clang:

clang version 10.0.0-4ubuntu1 
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin

[SteveBronder]

Agree with documenting behavior and keeping code asis

[deveshvaidyaofficial]

For this issue can a prompt be shown to the users to be aware of the new functionality, Hasn't this bug been there for quite some time? I feel a solution beneficial for all stakeholders can surely be found..

[SteveBronder]

I think the answer is to just update the docs for dims in the stan docs

https://github.com/stan-dev/docs