[R] solve() function freezes CLI in GNU R 3.6.3

[Jeff Newmiller]

Depending on reproducibility in the least significant bits of floating point calculations is a bad practice. Just because you decide based on this one example that one implementation of BLAS is better than another does not mean that will be true for all specific examples. IMO you are drawing conclusions on data that is effectively random and should change your definition of "sufficient to the task".

On May 13, 2020 11:29:33 AM PDT, Rasmus Liland <jral using posteo.no> wrote:
>On 2020-05-13 13:04 -0400, J C Nash wrote:
>> On 2020-05-13 11:28 a.m., Rasmus Liland wrote:
>> > 
>> > I get another solution on my Linux i7-7500U 
>> > 
>> > > D %*% solve(D)
>> >              [,1] [,2]
>> > [1,] 1.000000e+00    0
>> > [2,] 8.881784e-16    1
>> > > sessionInfo()
>> > BLAS:   /usr/lib/libopenblasp-r0.3.9.so
>> > LAPACK: /usr/lib/liblapack.so.3.9.0
>> 
>> Note that my sessionInfo() gave
>> 
>> R version 4.0.0 (2020-04-24)
>> Platform: x86_64-pc-linux-gnu (64-bit)
>> Running under: Linux Mint 19.3
>> 
>> Matrix products: default
>> BLAS:   /usr/lib/x86_64-linux-gnu/blas/libblas.so.3.7.1
>> LAPACK: /usr/lib/x86_64-linux-gnu/lapack/liblapack.so.3.7.1
>> 
>> So you have an older R but newer libraries, and the libblas is
>> a different one.
>> 
>> Given the output is very similar, and within the rounding
>> margins of the double arithmetic, this looks like the
>> libraries are very slightly different. I suppose I should
>> be more inquisitive and try to seek out the changelog or other
>> description of the differences, but ...
>> 
>> JN
>
>Dear JN,
>
>I was thinking BLAS could be changed to 
>OpenBLAS, apparently not:
>
>If I switch from OpenBLAS back to regular 
>BLAS, the output is as expected ... I thought 
>OpenBLAS should be a real alternative to BLAS 
>in many cases, but not in this example?
>
>> D %*% solve(D)
>     [,1]         [,2]
>[1,]    1 1.110223e-16
>[2,]    0 1.000000e+00
>> sessionInfo()
>R version 3.6.3 (2020-02-29)
>Platform: x86_64-pc-linux-gnu (64-bit)
>Running under: Arch Linux
>
>Matrix products: default
>BLAS:   /usr/lib/libblas.so.3.9.0
>LAPACK: /usr/lib/liblapack.so.3.9.0
>
>Best,
>Rasmus
>
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-- 
Sent from my phone. Please excuse my brevity.