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Decoherence and MWI in Nature

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  • Günther Greindl
    There is an article in Nature by Philip Ball about decoherence and many good references about MWI/decoherence related experiments:
    Message 1 of 20 , May 1 3:45 AM
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      There is an article in Nature by Philip Ball about decoherence and many
      good references about MWI/decoherence related experiments:

      http://www.nature.com/news/2008/080430//full/453022a.html

      A commentor also raises an interesting alternative explanation to MWI -
      non-linearity at mesoscopic scale:

      "Decoherence by itself cannot explain the quantum-classical transition;
      it must be supplemented by the many-worlds interpretation. This is
      because while decoherence destroys interference amongst alternatives, it
      preserves superpositions, since it works within the framework of linear
      quantum mechanics.

      An alternate explanation for emergent classicality, not ruled out by
      experiments, is that quantum mechanics is modified, say to a non-linear
      theory, on mesoscopic scales.

      As a result of the non-linearity, the life-time of a quantum
      superposition becomes dependent on the number of degrees of freedom of
      the system, and goes to zero for large systems. Experiments should be
      attempted, to test for the presence/absence of non-linearity in quantum
      mechanics on the mesoscopic scale."
      (T. P. Singh, Tata Institute of Fundamental Research, Mumbai)


      Does anybody know of experiments/theories shedding light on this
      alternative possibility?


      Cheers,
      Günther



      --
      Günther Greindl
      Department of Philosophy of Science
      University of Vienna
      guenther.greindl@...
      http://www.univie.ac.at/Wissenschaftstheorie/

      Blog: http://dao.complexitystudies.org/
      Site: http://www.complexitystudies.org
    • Marchal Bruno
      Hmmm... We know that if the SWE is correct, then, phenomenologically it is as if a cut exists, between us and what we observe. Decoherence + Everett (+ comp
      Message 2 of 20 , May 1 11:22 AM
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        Hmmm... We know that if the SWE is correct, then, phenomenologically it is as if a cut exists, between us and what we observe. Decoherence + Everett (+ comp like hyp in the cognitive science) explains exactly that. So why should we suppose that the mesoscopic level would begin to fail SWE? At least for those who say that non linearity occurs in consciousness, we can understand the "apparent evidences", (but then we can remember that Everett , and some comp like hyp, explains those "apparences"or at least the talk on those apparences made by the physicist (assuming the physicist is obeying himself to the SWE, a natural (monistic and non-anthropic) assumption).

        Bruno

        Günther Greindl wrote:

        >There is an article in Nature by Philip Ball about decoherence and many
        >good references about MWI/decoherence related experiments:
        >
        >http://www.nature.com/news/2008/080430//full/453022a.html
        >
        >A commentor also raises an interesting alternative explanation to MWI -
        >non-linearity at mesoscopic scale:
        >
        >"Decoherence by itself cannot explain the quantum-classical transition;
        >it must be supplemented by the many-worlds interpretation. This is
        >because while decoherence destroys interference amongst alternatives, it
        >preserves superpositions, since it works within the framework of linear
        >quantum mechanics.
        >
        >An alternate explanation for emergent classicality, not ruled out by
        >experiments, is that quantum mechanics is modified, say to a non-linear
        >theory, on mesoscopic scales.
        >
        >As a result of the non-linearity, the life-time of a quantum
        >superposition becomes dependent on the number of degrees of freedom of
        >the system, and goes to zero for large systems. Experiments should be
        >attempted, to test for the presence/absence of non-linearity in quantum
        >mechanics on the mesoscopic scale."
        >(T. P. Singh, Tata Institute of Fundamental Research, Mumbai)
        >
        >
        >Does anybody know of experiments/theories shedding light on this
        >alternative possibility?
        >
        >
        >Cheers,
        >Günther
        >
        >
        >
        >--
        >Günther Greindl
        >Department of Philosophy of Science
        >University of Vienna
        >guenther.greindl@...
        >http://www.univie.ac.at/Wissenschaftstheorie/
        >
        >Blog: http://dao.complexitystudies.org/
        >Site: http://www.complexitystudies.org
        >
        >
      • Russell Standish
        ... Weinberg looked at nonlinear extensions to QM, but found it difficult to reconcile with other aspects of physics (eg causality IIRC). I think the ref
        Message 3 of 20 , May 1 4:55 PM
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          On Thu, May 01, 2008 at 12:45:23PM +0200, Günther Greindl wrote:
          >
          > Does anybody know of experiments/theories shedding light on this
          > alternative possibility?
          >
          >
          > Cheers,
          > Günther
          >

          Weinberg looked at nonlinear extensions to QM, but found it difficult
          to reconcile with other aspects of physics (eg causality IIRC). I
          think the ref (although its been a while, so I could be wrong) is

          @Article{Weinberg89,
          author = {Steven Weinberg},
          title = {Testing Quantum Mechanics},
          journal = {Annals of Physics},
          year = 1989,
          volume = 194,
          pages = {336--386}
          }

          Available as PDF here
          http://ccdb4fs.kek.jp/cgi-bin/img_index?8905562

          And another paper on the same subject is here

          http://www.hep.princeton.edu/~mcdonald/examples/QM/weinberg_prl_62_485_89.pdf

          Of course in my derivation, I get linearity from first principles, but
          something like the MWI is one of those first principles. My gut feeling
          is that I would be totally surprised if nonlinear quantum effects were
          found, but if it were, it would be utterly catastrophic for the MWI.

          Cheers

          --

          ----------------------------------------------------------------------------
          A/Prof Russell Standish Phone 0425 253119 (mobile)
          Mathematics
          UNSW SYDNEY 2052 hpcoder@...
          Australia http://www.hpcoders.com.au
          ----------------------------------------------------------------------------
        • scott slaughter
          Does this experiment produce results that are nonlinear on the quantum level ? http://www.mpq.mpg.de/cms/mpq/en/news/press/pdf/2008/PMeng__13_4_rempe_final.pdf
          Message 4 of 20 , May 2 5:07 PM
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            Does this experiment produce results that are nonlinear on the quantum level
            ?

            http://www.mpq.mpg.de/cms/mpq/en/news/press/pdf/2008/PMeng__13_4_rempe_final.pdf

            Clarkdog

            On Thu, May 1, 2008 at 7:55 PM, Russell Standish <list@...>
            wrote:

            > On Thu, May 01, 2008 at 12:45:23PM +0200, Günther Greindl wrote:
            > >
            > > Does anybody know of experiments/theories shedding light on this
            > > alternative possibility?
            > >
            > >
            > > Cheers,
            > > Günther
            > >
            >
            > Weinberg looked at nonlinear extensions to QM, but found it difficult
            > to reconcile with other aspects of physics (eg causality IIRC). I
            > think the ref (although its been a while, so I could be wrong) is
            >
            > @Article{Weinberg89,
            > author = {Steven Weinberg},
            > title = {Testing Quantum Mechanics},
            > journal = {Annals of Physics},
            > year = 1989,
            > volume = 194,
            > pages = {336--386}
            > }
            >
            > Available as PDF here
            > http://ccdb4fs.kek.jp/cgi-bin/img_index?8905562
            >
            > And another paper on the same subject is here
            >
            >
            > http://www.hep.princeton.edu/~mcdonald/examples/QM/weinberg_prl_62_485_89.pdf
            >
            > Of course in my derivation, I get linearity from first principles, but
            > something like the MWI is one of those first principles. My gut feeling
            > is that I would be totally surprised if nonlinear quantum effects were
            > found, but if it were, it would be utterly catastrophic for the MWI.
            >
            > Cheers
            >
            > --
            >
            > ----------------------------------------------------------
            > A/Prof Russell Standish Phone 0425 253119 (mobile)
            > Mathematics
            > UNSW SYDNEY 2052 hpcoder@... <hpcoder%40hpcoders.com.au>
            > Australia http://www.hpcoders.com.au
            > ----------------------------------------------------------
            >
            >
            >


            [Non-text portions of this message have been removed]
          • Alan Forrester
            ... http://www.mpq.mpg.de/cms/mpq/en/news/press/pdf/2008/PMeng__13_4_rempe_final.pdf No. Sometimes if you look at the evolution of a quantum system that is
            Message 5 of 20 , May 3 11:10 AM
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              --- scott slaughter <slaughterenator@...> wrote:

              > Does this experiment produce results that are nonlinear on the quantum
              > level
              > ?
              >
              >
              http://www.mpq.mpg.de/cms/mpq/en/news/press/pdf/2008/PMeng__13_4_rempe_final.pdf

              No. Sometimes if you look at the evolution of a quantum system that is
              interacting with other systems its evolution will look non-linear because
              you're neglecting the effect of the other systems.

              Alan


              __________________________________________________________
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            • scott slaughter
              thanks clarkdog On Sat, May 3, 2008 at 2:10 PM, Alan Forrester ... [Non-text portions of this message have been removed]
              Message 6 of 20 , May 3 11:48 AM
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                thanks

                clarkdog

                On Sat, May 3, 2008 at 2:10 PM, Alan Forrester <alan_forrester2@...>
                wrote:

                >
                > --- scott slaughter <slaughterenator@...<slaughterenator%40gmail.com>>
                > wrote:
                >
                > > Does this experiment produce results that are nonlinear on the quantum
                > > level
                > > ?
                > >
                > >
                >
                > http://www.mpq.mpg.de/cms/mpq/en/news/press/pdf/2008/PMeng__13_4_rempe_final.pdf
                >
                > No. Sometimes if you look at the evolution of a quantum system that is
                > interacting with other systems its evolution will look non-linear because
                > you're neglecting the effect of the other systems.
                >
                > Alan
                >
                > __________________________________________________________
                > Sent from Yahoo! Mail.
                > A Smarter Email http://uk.docs.yahoo.com/nowyoucan.html
                >
                >
                >


                [Non-text portions of this message have been removed]
              • Günther Greindl
                Dear Russell, thanks for the papers! Cheers, Günther
                Message 7 of 20 , May 4 12:51 PM
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                  Dear Russell,

                  thanks for the papers!

                  Cheers,
                  Günther

                  Russell Standish wrote:
                  >
                  >
                  > On Thu, May 01, 2008 at 12:45:23PM +0200, Günther Greindl wrote:
                  > >
                  > > Does anybody know of experiments/ theories shedding light on this
                  > > alternative possibility?
                  > >
                  > >
                  > > Cheers,
                  > > Günther
                  > >
                  >
                  > Weinberg looked at nonlinear extensions to QM, but found it difficult
                  > to reconcile with other aspects of physics (eg causality IIRC). I
                  > think the ref (although its been a while, so I could be wrong) is
                  >
                  > @Article{Weinberg89 ,
                  > author = {Steven Weinberg},
                  > title = {Testing Quantum Mechanics},
                  > journal = {Annals of Physics},
                  > year = 1989,
                  > volume = 194,
                  > pages = {336--386}
                  > }
                  >
                  > Available as PDF here
                  > http://ccdb4fs. kek.jp/cgi- bin/img_index? 8905562
                  > <http://ccdb4fs.kek.jp/cgi-bin/img_index?8905562>
                  >
                  > And another paper on the same subject is here
                  >
                  > http://www.hep. princeton. edu/~mcdonald/ examples/ QM/weinberg_
                  > prl_62_485_ 89.pdf
                  > <http://www.hep.princeton.edu/~mcdonald/examples/QM/weinberg_prl_62_485_89.pdf>
                  >
                • Günther Greindl
                  Bruno, in principle I agree with your analysis - it s just that one should not rest to criticise one s one assumptions, and if there are other models which
                  Message 8 of 20 , May 4 12:59 PM
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                    Bruno,

                    in principle I agree with your analysis - it's just that one should not
                    rest to criticise one's one assumptions, and if there are other models
                    which "fit the data" then one should be careful about ontological
                    commitments one makes (as, for instance, positing many worlds)

                    The suggestion of nonlinear QM (which I don't think will show up, but it
                    has to be considered) is then parsimonious in it's ontology (one world)
                    without introducing anthropocentric reasoning (no consciousness or
                    whatever required for collapse).

                    A middle ground would be something like this:

                    http://hanson.gmu.edu/mangledworlds.html

                    (QM stays linear, but some worlds are destroyed via interference - to
                    recover Born's rule)

                    Cheers,
                    Günther


                    Marchal Bruno wrote:
                    >
                    >
                    > Hmmm... We know that if the SWE is correct, then, phenomenologically it
                    > is as if a cut exists, between us and what we observe. Decoherence +
                    > Everett (+ comp like hyp in the cognitive science) explains exactly
                    > that. So why should we suppose that the mesoscopic level would begin to
                    > fail SWE? At least for those who say that non linearity occurs in
                    > consciousness, we can understand the "apparent evidences", (but then we
                    > can remember that Everett , and some comp like hyp, explains those
                    > "apparences" or at least the talk on those apparences made by the
                    > physicist (assuming the physicist is obeying himself to the SWE, a
                    > natural (monistic and non-anthropic) assumption).
                    >
                    > Bruno
                    >
                    > Günther Greindl wrote:
                    >
                    > >There is an article in Nature by Philip Ball about decoherence and many
                    > >good references about MWI/decoherence related experiments:
                    > >
                    > >http://www.nature com/news/ 2008/080430/ /full/453022a. html
                    > <http://www.nature.com/news/2008/080430//full/453022a.html>
                    > >
                    > >A commentor also raises an interesting alternative explanation to MWI -
                    > >non-linearity at mesoscopic scale:
                    > >
                    > >"Decoherence by itself cannot explain the quantum-classical transition;
                    > >it must be supplemented by the many-worlds interpretation. This is
                    > >because while decoherence destroys interference amongst alternatives, it
                    > >preserves superpositions, since it works within the framework of linear
                    > >quantum mechanics.
                    > >
                    > >An alternate explanation for emergent classicality, not ruled out by
                    > >experiments, is that quantum mechanics is modified, say to a non-linear
                    > >theory, on mesoscopic scales.
                    > >
                    > >As a result of the non-linearity, the life-time of a quantum
                    > >superposition becomes dependent on the number of degrees of freedom of
                    > >the system, and goes to zero for large systems. Experiments should be
                    > >attempted, to test for the presence/absence of non-linearity in quantum
                    > >mechanics on the mesoscopic scale."
                    > >(T. P. Singh, Tata Institute of Fundamental Research, Mumbai)
                    > >
                    > >
                    > >Does anybody know of experiments/ theories shedding light on this
                    > >alternative possibility?
                    > >
                    > >
                    > >Cheers,
                    > >Günther
                    > >
                    > >
                    > >
                    > >--
                    > >Günther Greindl
                    > >Department of Philosophy of Science
                    > >University of Vienna
                    > >guenther.greindl@ univie.ac. at <mailto:guenther.greindl%40univie.ac.at>
                    > >http://www.univie ac.at/Wissenscha ftstheorie/
                    > <http://www.univie.ac.at/Wissenschaftstheorie/>
                    > >
                    > >Blog: http://dao.complexi tystudies. org/
                    > <http://dao.complexitystudies.org/>
                    > >Site: http://www.complexi tystudies. org
                    > <http://www.complexitystudies.org>
                    > >
                    > >
                    >
                    >

                    --
                    Günther Greindl
                    Department of Philosophy of Science
                    University of Vienna
                    guenther.greindl@...
                    http://www.univie.ac.at/Wissenschaftstheorie/

                    Blog: http://dao.complexitystudies.org/
                    Site: http://www.complexitystudies.org
                  • Gary Oberbrunner
                    ... Very interesting. But why does he say this: The big problem with the many worlds view is that no one has really shown how the usual linear rule in
                    Message 9 of 20 , May 5 7:08 AM
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                      Günther Greindl wrote:
                      > A middle ground would be something like this:
                      >
                      > http://hanson.gmu.edu/mangledworlds.html
                      > <http://hanson.gmu.edu/mangledworlds.html>
                      >
                      > (QM stays linear, but some worlds are destroyed via interference - to
                      > recover Born's rule)

                      Very interesting. But why does he say this:

                      "The big problem with the many worlds view is that no one has really
                      shown how the usual linear rule in disguise can reproduce Born
                      probability rule evolution. Many worlders who try to derive the Born
                      rule from symmetry assumptions often forget that there is no room for
                      "choosing" a probability rule to go with the many worlds view; if all
                      evolution is the usual linear deterministic rule in disguise, then aside
                      from unknown initial or boundary conditions, all experimentally
                      verifiable probabilities must be calculable from within the theory. So
                      what do theory calculations say? After a world splits a finite number of
                      times into a large but finite number of branch worlds, the vast majority
                      of those worlds will not have seen frequencies of outcomes near that
                      given by the Born rule, but will instead have seen frequencies near an
                      equal probability rule. If the probability of an outcome is the fraction
                      of worlds that see an outcome, then the many worlds view seems to
                      predict equal probabilities, not Born probabilities."


                      I don't understand exactly what he's getting at, but it seems like he's
                      assuming a binary split at each measurement, i.e. exactly two worlds
                      rather than a continuum of worlds at each point with measures according
                      to the Born rule. As I understand MWI, it seems to predict the Born
                      rule fine, but IANAP. Anyone care to comment?

                      --
                      Gary Oberbrunner
                    • Russell Standish
                      ... I never really understood Hanson s mangled worlds. But given that Born s rule appears as a first person effect out of the full 3rd person many worlds (at
                      Message 10 of 20 , May 5 3:56 PM
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                        On Sun, May 04, 2008 at 09:59:31PM +0200, Günther Greindl wrote:
                        > Bruno,
                        >
                        > in principle I agree with your analysis - it's just that one should not
                        > rest to criticise one's one assumptions, and if there are other models
                        > which "fit the data" then one should be careful about ontological
                        > commitments one makes (as, for instance, positing many worlds)
                        >
                        > The suggestion of nonlinear QM (which I don't think will show up, but it
                        > has to be considered) is then parsimonious in it's ontology (one world)
                        > without introducing anthropocentric reasoning (no consciousness or
                        > whatever required for collapse).
                        >
                        > A middle ground would be something like this:
                        >
                        > http://hanson.gmu.edu/mangledworlds.html
                        >
                        > (QM stays linear, but some worlds are destroyed via interference - to
                        > recover Born's rule)
                        >
                        > Cheers,
                        > Günther
                        >

                        I never really understood Hanson's mangled worlds. But given that
                        Born's rule appears as a first person effect out of the full 3rd
                        person many worlds (at least if my reasoning is correct), I never paid
                        it too much credence anyway.

                        --

                        ----------------------------------------------------------------------------
                        A/Prof Russell Standish Phone 0425 253119 (mobile)
                        Mathematics
                        UNSW SYDNEY 2052 hpcoder@...
                        Australia http://www.hpcoders.com.au
                        ----------------------------------------------------------------------------
                      • Bruno Marchal
                        Hi Günther, ... Sure. It is just that without an independent reason to expect non linearity in the mesoscopic, it will look (a bit like GRW theory) like an ad
                        Message 11 of 20 , May 6 3:53 AM
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                          Hi Günther,

                          Le 04-mai-08, à 21:59, Günther Greindl a écrit :

                          > Bruno,
                          >
                          > in principle I agree with your analysis - it's just that one should
                          > not
                          > rest to criticise one's one assumptions, and if there are other models
                          > which "fit the data" then one should be careful about ontological
                          > commitments one makes (as, for instance, positing many worlds)


                          Sure. It is just that without an independent reason to expect non
                          linearity in the mesoscopic, it will look (a bit like GRW theory) like
                          an ad hoc way to (re)introduce the collapse.




                          >
                          > The suggestion of nonlinear QM (which I don't think will show up, but
                          > it
                          > has to be considered) is then parsimonious in it's ontology (one
                          > world)
                          > without introducing anthropocentric reasoning (no consciousness or
                          > whatever required for collapse).


                          Russell has pointed on Weinberg paper. What Weinberg has shown is that
                          non linearity cannot exclude the many worlds: it makes them worst in
                          the sense that if QM is slightly non linear, then not only there are
                          many interfering worlds, but then interaction in between world is made
                          possible, and it is this which put in jeopardy the traditional
                          statistical foundation of thermodynamic.
                          To suppress the many worlds from QM, you have to "delinearize" QM so
                          much that it is not clear how to recover even finite sets of
                          experimental physical data.
                          ... and then remember that I suggest that once we accept the
                          independent belief (independent from QM) in the computationalist
                          hypothesis in the cognitive sciences, then just arithmetic itself
                          should be interpreted from inside as a many interfering
                          "worlds/states/minds" reality.



                          >
                          > A middle ground would be something like this:
                          >
                          > http://hanson.gmu.edu/mangledworlds.html
                          >
                          > (QM stays linear, but some worlds are destroyed via interference - to
                          > recover Born's rule)


                          I have probably read this too quickly but I didn't grasp what Hanson
                          means by inexact decoherence. Actually, I am already convinced by
                          Wallace (search in the Stanford Archive for qunatum Physics). Or (Even
                          just Everett long paper + Gleason theorem).


                          Have a good day,

                          Bruno
                        • Russell Standish
                          ... The probabilities all depend on what is measured. If I choose to measure the angle of a particle after having collided with a massive target, I would
                          Message 12 of 20 , May 6 3:43 PM
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                            On Mon, May 05, 2008 at 10:08:26AM -0400, Gary Oberbrunner wrote:
                            > Günther Greindl wrote:
                            > > A middle ground would be something like this:
                            > >
                            > > http://hanson.gmu.edu/mangledworlds.html
                            > > <http://hanson.gmu.edu/mangledworlds.html>
                            > >
                            > > (QM stays linear, but some worlds are destroyed via interference - to
                            > > recover Born's rule)
                            >
                            > Very interesting. But why does he say this:
                            >
                            > "The big problem with the many worlds view is that no one has really
                            > shown how the usual linear rule in disguise can reproduce Born
                            > probability rule evolution. Many worlders who try to derive the Born
                            > rule from symmetry assumptions often forget that there is no room for
                            > "choosing" a probability rule to go with the many worlds view; if all
                            > evolution is the usual linear deterministic rule in disguise, then aside
                            > from unknown initial or boundary conditions, all experimentally
                            > verifiable probabilities must be calculable from within the theory. So
                            > what do theory calculations say? After a world splits a finite number of
                            > times into a large but finite number of branch worlds, the vast majority
                            > of those worlds will not have seen frequencies of outcomes near that
                            > given by the Born rule, but will instead have seen frequencies near an
                            > equal probability rule. If the probability of an outcome is the fraction
                            > of worlds that see an outcome, then the many worlds view seems to
                            > predict equal probabilities, not Born probabilities."
                            >
                            >
                            > I don't understand exactly what he's getting at, but it seems like he's
                            > assuming a binary split at each measurement, i.e. exactly two worlds
                            > rather than a continuum of worlds at each point with measures according
                            > to the Born rule. As I understand MWI, it seems to predict the Born
                            > rule fine, but IANAP. Anyone care to comment?
                            >
                            > --
                            > Gary Oberbrunner

                            The probabilities all depend on what is measured. If I choose to
                            measure the angle of a particle after having collided with a massive
                            target, I would expect that forward angles to be much more probable
                            than reverse angles for instance.

                            The connection with equiprobability must be via the uniform measure on
                            bitstrings in something like my all strings ensemble, but the MWI is
                            at a much higher level of abstraction than that.

                            My understanding based on van Esch's paper in 2005 is that the MWI per se is
                            insuffucient to generate the Born rule. But then Youness mentioned
                            Gleason's theorem as possibly indicating the opposite. More reading of
                            the literature is require, methinks (as if I don't have enough already!).


                            --

                            ----------------------------------------------------------------------------
                            A/Prof Russell Standish Phone 0425 253119 (mobile)
                            Mathematics
                            UNSW SYDNEY 2052 hpcoder@...
                            Australia http://www.hpcoders.com.au
                            ----------------------------------------------------------------------------
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