Oleg Kobchenko wrote:
>
> What would be the J equivalent to Javascript
>
> 11259375.071111083.toString(16)
> abcdef.123456
>
> That is the "inverse" of
>
> 0j10 ": 16babcdef.123456
> 11259375.0711110830
>
Short and unsatisfactory answer would be: "it depends on
what abcdef.123456 means." It is presumably a floating
point (FP) number, but in which representation?
Of course, all this is IEEE standardized nowadays, but your
example reminds me of a FORTRAN programming course I took
some long time ago where I learned that FP numbers are
represented in base 16.
I'd like then to contribute a bit of code for the LAPACK
add-on for J, namely a call to LAPACK's DLAMCH function in
the following small file '~addons/math/lapack/dlamch.ijs' ,
based on your '~addons/math/lapack/lapack.ijs'
------------------------------------------------------->cut here<---------
NB. dlamch determines double precision machine parameters.
coclass'jlapack'
NB. Use: double dlamch p (function)
NB.
NB. p is a character or a string (only the first letter is important.)
NB. The function returns a double-precision value corresponding
NB. to the parameter p (see dlamchAll below.)
dlamch=: 3 : 0
if.{.y e.'EeSsBbPpNnRrMmUuLlOo'do.
>{.(dll,'dlamch_ + d *')cd {.,each y
else.
error y;'not a valid argument for dlamch.'
end.
)
dlamchAll=: 3 : 0 NB.
p=:,:'Eps -- relative machine precision'
p=:p,'Safe minimum, such that 1/sfmin does not overflow'
p=:p,'Base of the machine'
p=:p,'Precision (Eps*Base)'
p=:p,'Number of (base) digits in the mantissa'
p=:p,'Rnd -- (1.0 when rounding occurs in addition, 0.0 otherwise)'
p=:p,'Minimum exponent before (gradual) underflow (emin)'
p=:p,'Underflow threshold - Base**(emin-1)'
p=:p,'Largest exponent before overflow'
p=:p,'Overflow threshold - (Base**emax)*(1-Eps)'
(] ; dlamch_jlapack_)"1 p
)
------------------------------------------------------->cut here<---------
NB. One session:
require '~addons/math/lapack/lapack.ijs'
require '~addons/math/lapack/dlamch.ijs'
dlamch_jlapack_'b' NB. Base
2
dlamch_jlapack_'n' NB. Number of bits in mantissa.
53
dlamchAll_jlapack_'' NB. Gives a table (not shown here)
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