Fix R CMD check error on M1mac

[kwstat]

From CRAN:

Check: tests
Result: ERROR
     Running ‘testthat.R’ [1s/1s]
    Running the tests in ‘tests/testthat.R’ failed.
    Last 13 lines of output:
     PC 5 starting column: 2..
     ══ Skipped tests ═══════════════════════════════════════════════════════════════
     • empty test (2)
    
     ══ Failed tests ════════════════════════════════════════════════════════════════
     ── Failure (test-uscrime.R:68:3): SVD, NIPALS and EMPCA results match for complete uscrime data ──
     `avg_angle` is not strictly less than `tol`. Difference: NaN
     Backtrace:
     █
     1. └─nipals:::expect_aligned(m1s$u, m1e$scores) test-uscrime.R:68:2
     2. └─testthat::expect_lt(avg_angle, tol) setup-expectations.R:22:2
    
     [ FAIL 1 | WARN 1 | SKIP 2 | PASS 27 ]
     Error: Test failures
     Execution halted
Flavor: r-release-macos-arm64

Note: arm64 (aka 'Apple Silicon' aka 'M1') Mac.

[kwstat]

rhub::platforms() gives (among others):

macos-highsierra-release:
  macOS 10.13.6 High Sierra, R-release, brew
macos-highsierra-release-cran:
  macOS 10.13.6 High Sierra, R-release, CRAN's setup
macos-m1-bigsur-release:
  Apple Silicon (M1), macOS 11.6 Big Sur, R-release

[kwstat]

This was painfull hard to diagnose, so here are some things I learned.

1. This error was only happening on Mac M1. You can test only that platform on Rhub:

rhub::check("nipals_0.7.tar.gz", platform = "macos-m1-bigsur-release")

2. Rhub truncates the test output to the last 13 lines. You can get around that by setting an environment variable to disable truncation:

rhub::check("nipals_0.7.tar.gz", env_vars = c(`_R_CHECK_TESTS_NLINES_` = '0'),
            platform = "macos-m1-bigsur-release")

3. Due to floating point error, the dot product of two nearly-parallel vectors can end up outside [-1,1]. Previously I checked for this condition before calling acos() to find the angle between the vectors:

acos( abs(dotprod) - .Machine$double.eps )

But on this Mac M1 machine for this problem, print(dotprod, digits=17) = -1.00000000000000044 and subtracting .Machine$double.eps was not sufficient to bring the value inside [-1,1].

(abs(-1.00000000000000044) - .Machine$double.eps ) < 1
# FALSE

So I switched to ensuring the value is inside [-1,1] with

pmin(abs(dotprod), 1)