borglab/gtsam: Release 4.2a9

This is hopefully the last 4.2 pre-release. I had planned to cut 4.2 this weekend but there were still apparently some issues with the wrapper when used in Georgia tech's CS 3630 course (325 students using GTSAM) and so I'd rather wait another week for these things to settle down. In the meantime, though, we needed a pre-release so %pip install gtbook works on Google Colab and installs 4.2a9 in the process. All works now, as evidenced at roboticsbook.org.

The biggest changes are:

• moved away from boost utilities to c++ initializers in all tests and examples.
• a cleaned up and correctly working hybrid inference framework. Thanks @varunagrawal and @ProfFan !
• template-magical NoiseModelFactorN which allows an arbitrary number of variables connected to factors. Thanks @gchenfc !
• several important bug-fixes and edits, by many new contributors, listed below:

• @nkhedekar made their first contribution in https://github.com/borglab/gtsam/pull/1330
• @MigVega made their first contribution in https://github.com/borglab/gtsam/pull/1331
• @ulterzlw made their first contribution in https://github.com/borglab/gtsam/pull/1340
• @jrpowers made their first contribution in https://github.com/borglab/gtsam/pull/1361
• @stefangachter made their first contribution in https://github.com/borglab/gtsam/pull/1296
• @njayakumar3 made their first contribution in https://github.com/borglab/gtsam/pull/789
• @BrettRD made their first contribution in https://github.com/borglab/gtsam/pull/1376
• @acowley made their first contribution in https://github.com/borglab/gtsam/pull/1381

• Add an expression for normalize() by @nkhedekar in https://github.com/borglab/gtsam/pull/1330
• Update README.md by @MigVega in https://github.com/borglab/gtsam/pull/1331
• Hybrid Elimination by @varunagrawal in https://github.com/borglab/gtsam/pull/1339
• Fixed Jacobian in python CustomFactorExample by @ulterzlw in https://github.com/borglab/gtsam/pull/1340
• Hybrid Mixture Error by @varunagrawal in https://github.com/borglab/gtsam/pull/1318
• Hybrid Multifrontal by @varunagrawal in https://github.com/borglab/gtsam/pull/1323
• NoiseModelFactorN - fixed-number of variables >6 by @gchenfc in https://github.com/borglab/gtsam/pull/947
• GaussianConditional logDeterminant by @varunagrawal in https://github.com/borglab/gtsam/pull/1345
• Replace NoiseModelFactor1 in with NoiseModelFactorN in pre-made factors by @gchenfc in https://github.com/borglab/gtsam/pull/1344
• Hybrid Bayes Net sampling by @varunagrawal in https://github.com/borglab/gtsam/pull/1347
• Fix wrapper warnings by @varunagrawal in https://github.com/borglab/gtsam/pull/1348
• Update geometry.i : wrap multiplication of Rot3 and Unit3 by @akshay-krishnan in https://github.com/borglab/gtsam/pull/1302
• Sampling test for Hybrid Posterior by @varunagrawal in https://github.com/borglab/gtsam/pull/1346
• Some refactoring and new test by @dellaert in https://github.com/borglab/gtsam/pull/1349
• Add logDensity and evaluate to GaussianBN and HybridBN by @dellaert in https://github.com/borglab/gtsam/pull/1352
• Added convenience constructors and python wrappers by @dellaert in https://github.com/borglab/gtsam/pull/1353
• Wrap constructors for PreintegratedAhrsMeasurements by @varunagrawal in https://github.com/borglab/gtsam/pull/1354
• HybridValues specify continuous then discrete by @varunagrawal in https://github.com/borglab/gtsam/pull/1355
• Likelihoods and other improvements by @dellaert in https://github.com/borglab/gtsam/pull/1356
• Proper Hybrid Elimination by @varunagrawal in https://github.com/borglab/gtsam/pull/1319
• Test on ratio by @dellaert in https://github.com/borglab/gtsam/pull/1357
• Hybrid Improvements by @varunagrawal in https://github.com/borglab/gtsam/pull/1343
• Fix HybridGaussianFactorGraph error by @varunagrawal in https://github.com/borglab/gtsam/pull/1358
• Initializer list and insert/update chaining by @dellaert in https://github.com/borglab/gtsam/pull/1359
• Slightly expand Python API by @jrpowers in https://github.com/borglab/gtsam/pull/1361
• Check for native architecture and set GTSAM_COMPILE_OPTIONS_PUBLIC accordingly by @stefangachter in https://github.com/borglab/gtsam/pull/1296
• Fix hybrid tests by @varunagrawal in https://github.com/borglab/gtsam/pull/1363
• Fixed a few small issues... by @dellaert in https://github.com/borglab/gtsam/pull/1367
• Switch to EliminateDiscrete for max-product by @dellaert in https://github.com/borglab/gtsam/pull/1362
• Hybrid Serialization by @varunagrawal in https://github.com/borglab/gtsam/pull/1368
• Various fixes for Hybrid by @varunagrawal in https://github.com/borglab/gtsam/pull/1369
• Hybrid Elimination with Normalization Constant by @varunagrawal in https://github.com/borglab/gtsam/pull/1360
• Added *.bib file and started adding citations to README.md by @njayakumar3 in https://github.com/borglab/gtsam/pull/789
• Un-deprecate NoiseModelFactor1-6 and move X1 and key1-6 shortcuts to NoiseModelFactorN by @gchenfc in https://github.com/borglab/gtsam/pull/1370
• Two new tests, one with 5 modes by @dellaert in https://github.com/borglab/gtsam/pull/1371
• Simplified AP for HybridBayesNet by @dellaert in https://github.com/borglab/gtsam/pull/1372
• DefaultOrderingFunc in EliminationTraits by @varunagrawal in https://github.com/borglab/gtsam/pull/1373
• Big Re-"Factor" of Hybrid by @dellaert in https://github.com/borglab/gtsam/pull/1374
• More Expression wrappers by @BrettRD in https://github.com/borglab/gtsam/pull/1376
• Get rid of boost::assign by @dellaert in https://github.com/borglab/gtsam/pull/1375
• replace list_of with initializer list in TimeTBB.cpp by @kartikarcot in https://github.com/borglab/gtsam/pull/1379
• Harmonized error/logProbability in entire Factor/Conditional hierarchy by @dellaert in https://github.com/borglab/gtsam/pull/1380
• BatchFixedLagSmoother: add ability to limit warning debug prints by @acowley in https://github.com/borglab/gtsam/pull/1381
• Test and fix all conditionals by @dellaert in https://github.com/borglab/gtsam/pull/1386
• Some Hybrid Improvements by @varunagrawal in https://github.com/borglab/gtsam/pull/1387
• Hybrid/simplify by @dellaert in https://github.com/borglab/gtsam/pull/1388
• Correction to docs and lambdas by @varunagrawal in https://github.com/borglab/gtsam/pull/1390
• Switch pruning test to probabilities. by @dellaert in https://github.com/borglab/gtsam/pull/1394
• Deprecate filter by @dellaert in https://github.com/borglab/gtsam/pull/1397
• Fix examples that were using filter by @dellaert in https://github.com/borglab/gtsam/pull/1402
• Deprecated boost transform_iterators by @dellaert in https://github.com/borglab/gtsam/pull/1407
• Iterator for 4.2 by @dellaert in https://github.com/borglab/gtsam/pull/1417
• Fix (issue #1336) dangling pointer access violation. by @oicchris in https://github.com/borglab/gtsam/pull/1423
• Fix version... by @dellaert in https://github.com/borglab/gtsam/pull/1424
• 4.2 fixes by @varunagrawal in https://github.com/borglab/gtsam/pull/1425
• Patch ros package (branch: release/4.2) by @jlblancoc in https://github.com/borglab/gtsam/pull/1427
• Add missing header to fix gtbook by @dellaert in https://github.com/borglab/gtsam/pull/1429

Full Changelog: https://github.com/borglab/gtsam/compare/4.2a8...4.2a9