[Rd] nlminb with constraints failing on some platforms

[Ralf Stubner]

On 01.02.19 10:00, Martin Maechler wrote:
>> f <- function(x) sum( log(diff(x)^2+.01) + (x[1]-1)^2 )
>> opt <- nlminb(rep(0, 10), f, lower=-1, upper=3)
>> str(opt)
> List of 6
>  $ par        : num [1:10] 1 1 1 1 1 ...
>  $ objective  : num -41.4
>  $ convergence: int 0
>  $ iterations : int 66
>  $ evaluations: Named int [1:2] 96 830
>   ..- attr(*, "names")= chr [1:2] "function" "gradient"
>  $ message    : chr "relative convergence (4)"
>> xhat <- rep(1, 10)
>> all.equal(opt$par,         xhat,  tol=0) # good: 5.53 e-7
> [1] "Mean relative difference: 5.534757e-07"
>> all.equal(opt$objective, f(xhat), tol=0) # good: 1.8 e-12
> [1] "Mean relative difference: 1.816536e-12"
>> abs( opt$objective - f(xhat) ) < 1e-4  ## Must be TRUE
> [1] TRUE
>>
> 
> for me. Maybe others can quickly run the above  7 lines and report ?

Similar but not equal results for me:

> f <- function(x) sum( log(diff(x)^2+.01) + (x[1]-1)^2 )
> opt <- nlminb(rep(0, 10), f, lower=-1, upper=3)
> str(opt)
List of 6
 $ par        : num [1:10] 1 1 1 1 1 ...
 $ objective  : num -41.4
 $ convergence: int 0
 $ iterations : int 66
 $ evaluations: Named int [1:2] 96 830
  ..- attr(*, "names")= chr [1:2] "function" "gradient"
 $ message    : chr "relative convergence (4)"
> xhat <- rep(1, 10)
> all.equal(opt$par,         xhat,  tol=0) # good: 5.53 e-7
[1] "Mean relative difference: 3.266165e-07"
> all.equal(opt$objective, f(xhat), tol=0) # good: 1.8 e-12
[1] "Mean relative difference: 6.722005e-13"
> abs( opt$objective - f(xhat) ) < 1e-4  ## Must be TRUE
[1] TRUE


Setup:

* Debian Stable with gcc 6.2
* R 3.5.2 from CRAN repository
* OpenBLAS

Greetings
Ralf

-- 
Ralf Stubner
Senior Software Engineer / Trainer

daqana GmbH
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