Maths constants
in [Fortran]
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From: dpb on 22 Jan 2010 15:34 Dr Ivan D. Reid wrote: > On Fri, 22 Jan 2010 13:03:25 GMT, robin <robin_v(a)bigpond.com> > wrote in <xmh6n.2735$pv.1095(a)news-server.bigpond.net.au>: > >> I still use an HP 500C. >> The Kyocera died years ago, stripping its gears, after a short life. > >> That HP 500C is now 15 years old. > > I recently revived my [(hp)] HP-21, by buying a pack of two NiMH > AA batteries at Poundland[1] and slotting them into the battery holder in > place of the original NiCds. Works fine except the 2 key is a bit reluctant > to register. I bought it second hand (with a US power-supply switchable > between 115 and 230 V, and US pins, so I use a UK razor adaptor) when I was > doing my PhD -- about 1975. > > [1] No, don't ask how much they cost... I've done similar w/ my old HP-97 (the desktop version w/ printer, card reader, etc.) It all still functions except the rubber rollers for the paper feed are hard and slick so the paper doesn't feed well any longer. It's a joy given the size of the keys and display compared to anything at all newer and advancing eyesight... :) (Although the printing on the keys is smaller and smaller every day it seems... :( ) --
From: Gordon Sande on 22 Jan 2010 16:04 On 2010-01-22 16:34:40 -0400, dpb <none(a)non.net> said: > Dr Ivan D. Reid wrote: >> On Fri, 22 Jan 2010 13:03:25 GMT, robin <robin_v(a)bigpond.com> >> wrote in <xmh6n.2735$pv.1095(a)news-server.bigpond.net.au>: >> >>> I still use an HP 500C. >>> The Kyocera died years ago, stripping its gears, after a short life. >> >>> That HP 500C is now 15 years old. >> >> I recently revived my [(hp)] HP-21, by buying a pack of two NiMH >> AA batteries at Poundland[1] and slotting them into the battery holder in >> place of the original NiCds. Works fine except the 2 key is a bit reluctant >> to register. I bought it second hand (with a US power-supply switchable >> between 115 and 230 V, and US pins, so I use a UK razor adaptor) when I was >> doing my PhD -- about 1975. >> >> [1] No, don't ask how much they cost... > > I've done similar w/ my old HP-97 (the desktop version w/ printer, card > reader, etc.) It all still functions except the rubber rollers for the > paper feed are hard and slick so the paper doesn't feed well any longer. You can buy a small bottle of numble-numble-alcohol (isoproponol?) which will remove the glaze and soften the rubber rollers. It used to be in the do-it-yourself repair kits for laser printers. Did marvels for an old LaserWriter that was young at 10 years of age! If you have an ink cartridge refill outfit locally they might have it as a separate item. Otherwise look at the details of laser printer fixit kits. > It's a joy given the size of the keys and display compared to anything > at all newer and advancing eyesight... :) (Although the printing on > the keys is smaller and smaller every day it seems... :( )
From: Paul Hirose on 22 Jan 2010 16:43 "Richard Maine" <nospam(a)see.signature> wrote in message news:1jckfrv.w6yp2rh7f8q7N%nospam(a)see.signature... > The arc cosine of -1 is just about the worst case I can think of off > the > top of my head in terms of numerical robustness. Hint: look at the > arc > cosine of numbers very close to -1. If one is going to use trig > expressions for things like that, at least use them at decently > robust > points. That's independent of the language and the hardware - just > plain > numerics. I hear you. That's why I formerly used 2*acos(0d0) to obtain pi. But despite the theoretical objection to acos(-1d0), in practice I've never been able to find a problem. For instance, this program gives perfect zeros with Silverfrost FTN95 under Windows: program testpi implicit none ! double precision real kind integer, parameter :: dp = selected_real_kind(15) ! original poster's literal real (kind = dp), parameter :: pi = 3.141592653589793_dp print '(e10.2, a)', acos(-1.0_dp)-pi, ' = acos(-1)-pi' print '(e10.2, a)', 2*acos( 0.0_dp)-pi, ' = 2*acos( 0)-pi' print '(e10.2, a)', 2*asin( 1.0_dp)-pi, ' = 2*asin( 1)-pi' print '(e10.2, a)', 4*atan( 1.0_dp)-pi, ' = 4*atan( 1)-pi' end program testpi My mind is still open on this issue, though. Can anyone demonstrate an anomalous result with the above program? The only source code for acos() at hand here is P.J. Plauger, "The Standard C Library", 1992. His code treats -1 as a special case, and produces an accurate value for pi. For arguments other than special cases, he uses polynomials from one of the standard reference books (Cody and Waite). Let me make clear that my only claim is that acos(-1d0) has worked well for *me*, on Windows desktop machines. I put it out there because calculating pi at runtime from a trig function may be something new to the original poster. It's embarrassing to admit that I'd been programming for years before the idea occurred to me. -- Paul Hirose <jvcmz89uwf(a)earINVALIDthlink.net> To reply by email remove INVALID
From: Dr Ivan D. Reid on 22 Jan 2010 17:15 On Fri, 22 Jan 2010 21:04:01 GMT, Gordon Sande <g.sande(a)worldnet.att.net> wrote in <2010012217040116807-gsande(a)worldnetattnet>: >> I've done similar w/ my old HP-97 (the desktop version w/ printer, card >> reader, etc.) It all still functions except the rubber rollers for the >> paper feed are hard and slick so the paper doesn't feed well any longer. > You can buy a small bottle of numble-numble-alcohol (isoproponol?) which will > remove the glaze and soften the rubber rollers. Close. Isopropanol, or iso-propyl alcohol. Used as swabs before injections, etc, etc. I thought you guys called it rubbing alcohol, but my Chambers suggests rubbing alcohol is methylated spirits (denatured ethanol); maybe there's a transAtlantic schism there. -- Ivan Reid, School of Engineering & Design, _____________ CMS Collaboration, Brunel University. Ivan.Reid@[brunel.ac.uk|cern.ch] Room 40-1-B12, CERN KotPT -- "for stupidity above and beyond the call of duty".
From: Luka Djigas on 22 Jan 2010 17:57
On Fri, 22 Jan 2010 14:34:40 -0600, dpb <none(a)non.net> wrote: >It's a joy given the size of the keys and display compared to anything >at all newer and advancing eyesight... :) (Although the printing on the >keys is smaller and smaller every day it seems... :( ) I have the same problem with cell phones ... (No, 2x2mm in size are not "large keys"). Soon they'll be giving toothpicks with them, as "human interface devices". -- Luka |