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Alway use CwiseUnaryOp for .val() of var types - remove .val_op()#3351

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val-op
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Alway use CwiseUnaryOp for .val() of var types - remove .val_op()#3351
andrjohns wants to merge 8 commits into
developfrom
val-op

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@andrjohns

@andrjohns andrjohns commented Jul 21, 2026

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Summary

The .val() custom Eigen member always returns a CwiseUnaryView when called on a non-const input (as a CwiseUnaryView can be assigned to). However the CwiseUnaryView can result in compilation errors in some Eigen expressions and so the val_op() member was introduced as a way to explicitly request a CwiseUnaryOp (normally only called for const inputs).

For var types even though the var itself is non-const, the val_ member of the underlying vari is always const - so we actually always want a CwiseUnaryOp.

This PR replaces the val_op() implementation with template overloads for the val() implementation - only returning CwiseUnaryView for fvar inputs, otherwise returning a CwiseUnaryOp.

All usages of val_op() through the codebase have also been replaced with just val()

Tests

N/A - existing tests should successfully compile and run

Side Effects

N/A

Release notes

The .val() member function always returns a CwiseUnaryOp when called with a var type, the val_op() member function has been removed

Checklist

  • Copyright holder: Andrew Johnson

    The copyright holder is typically you or your assignee, such as a university or company. By submitting this pull request, the copyright holder is agreeing to the license the submitted work under the following licenses:
    - 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

WardBrian commented Jul 21, 2026

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The idea here seems sound, and your explanation of why the different functions existed in the first place is better than the doc we currently have IMO.

So, if you wouldn't mind updating that part of the doxygen to remove the mention of val_op and update our description of adj_op, I think this is good to go

@stan-buildbot

stan-buildbot commented Jul 22, 2026

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Name Old Result New Result Ratio Performance change( 1 - new / old )
gp_regr/gp_regr.stan 0.12 0.11 1.09 8.3% faster
gp_regr/gen_gp_data.stan 0.03 0.02 1.06 5.62% faster
arK/arK.stan 1.68 1.78 0.95 -5.52% slower
eight_schools/eight_schools.stan 0.06 0.06 1.04 3.83% faster
low_dim_gauss_mix_collapse/low_dim_gauss_mix_collapse.stan 8.95 8.59 1.04 3.97% faster
pkpd/one_comp_mm_elim_abs.stan 20.71 19.54 1.06 5.66% faster
pkpd/sim_one_comp_mm_elim_abs.stan 0.26 0.25 1.03 2.91% faster
sir/sir.stan 70.97 69.22 1.03 2.47% faster
gp_pois_regr/gp_pois_regr.stan 2.45 2.31 1.06 5.69% faster
low_dim_gauss_mix/low_dim_gauss_mix.stan 2.93 2.83 1.04 3.6% faster
irt_2pl/irt_2pl.stan 6.5 5.08 1.28 21.8% faster
arma/arma.stan 0.32 0.3 1.05 5.2% faster
garch/garch.stan 0.48 0.46 1.05 4.51% faster
low_dim_corr_gauss/low_dim_corr_gauss.stan 0.01 0.01 1.02 1.76% faster
performance.compilation 271.52 272.65 1.0 -0.42% slower
Mean result: 1.0524476721967695

Jenkins Console Log
Blue Ocean
Commit hash: 76c0fc94c2521a231ca73fbbf61dc5321170ecb7

Machine information No LSB modules are available. 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 6148 CPU @ 2.40GHz
Stepping: 4
CPU MHz: 2400.000
CPU max MHz: 3700.0000
CPU min MHz: 1000.0000
BogoMIPS: 4800.00
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 Itlb multihit: KVM: Mitigation: Split huge pages
Vulnerability L1tf: Mitigation; PTE Inversion; VMX conditional cache flushes, SMT vulnerable
Vulnerability Mds: Mitigation; Clear CPU buffers; SMT vulnerable
Vulnerability Meltdown: Mitigation; PTI
Vulnerability Mmio stale data: Mitigation; Clear CPU buffers; SMT vulnerable
Vulnerability Reg file data sampling: Not affected
Vulnerability Retbleed: Mitigation; 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; IBRS; IBPB conditional; STIBP conditional; RSB filling; PBRSB-eIBRS Not affected; BHI Not affected
Vulnerability Srbds: Not affected
Vulnerability Tsx async abort: Mitigation; Clear CPU buffers; SMT vulnerable
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 invpcid_single pti intel_ppin ssbd mba ibrs ibpb stibp tpr_shadow vnmi flexpriority ept vpid ept_ad fsgsbase tsc_adjust bmi1 hle avx2 smep bmi2 erms invpcid rtm 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 pku ospke 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

SteveBronder commented Jul 22, 2026

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One Q, should we just make the val_ of vari non-const? I get that we do not want to write to it, but if it is causing this odd pattern then maybe we should just get rid of that?

@WardBrian

WardBrian commented Jul 22, 2026

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One Q, should we just make the val_ of vari non-const? I get that we do not want to write to it, but if it is causing this odd pattern then maybe we should just get rid of that?

I think this PR is actually removing an odd pattern

@SteveBronder

SteveBronder commented Jul 22, 2026

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Oh! Sorry I was misreading things. Yes I think I like this PR

WardBrian
WardBrian requested changes Jul 22, 2026
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Doxygen still needs to be updated

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@WardBrian WardBrian WardBrian requested changes
@SteveBronder SteveBronder SteveBronder approved these changes

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@andrjohns @WardBrian @stan-buildbot @SteveBronder