An Interview with Bernie Alder
BA = Bernie Alder
GAM = George Michael
GAM: Today is March 5, 1997 and we are talking with Bernie Alder,
one of the earliest scientists to come to the Laboratory.
Bernie, please begin.
BA: To start right from the beginning, I was born in Germany as a
Swiss citizen in 1925 and, when Hitler came to power
in 1932 or 1933, I moved to Switzerland. And then I
came to the United States with my family in 1941, just
before the United States went into the war.
I did my undergraduate work at the University of
California, Berkeley (UCB) in Chemistry, and I was
interrupted by the war. I very nearly got into the
Manhattan Project; just slightly too young, they tried
to get me into it, but it wouldn't work. So I went into
the Navy and then came back and finished my
undergraduate degree at Berkeley in Chemistry in
1946. I got my Masters in Chemical Engineering in
1947 and then went to Cal Tech in 1948. I think that's
where I first got introduced to computers actually.
That's presumably what you're most interested in.
That's sort of an interesting story. I was working for
Kirkwood, who was the expert in statistical
mechanics, liquid theory, etc. We were trying to
figure out according to this theory whether hard
spheres had a phase transition to the solid phase and
we used a rather complicated nonlinear integral
equation that had to be solved and we could only
solve it on the computer. We only had IBM
mechanical computers that were programmed by a
plug board. Then I ran across a man named Stan
Frankel, who was the head of the computing
organization that had just been created at Cal Tech.
He came from Los Alamos. I think he was an
unrecognized genius in the business. We soon
realized that solving this nonlinear integral equation
didn't have a unique solution. We got into the
intermolecular instabilities. And then he or I or we
came up with the idea, it's hard to trace this down, to
use the Monte Carlo method to solve this hard sphere
problem. I don't know how much technical detail you
GAM: I'd like it all.
BA: We tried something that didn't initially work. We placed the
hard spheres into a box randomly to make a dense system. Of
course, when you try to place them in randomly,
and the thing that we realized almost immediately
was wrong, you have to try again and again. For example, if
you tried and it failed because it overlapped with one
of the existing spheres, you tried again until it fits.
Well, there are three things wrong with that. It isn't
quicker to do, you can easily show that
statistically it isn't correct and, thirdly, you can't get
very high densities by just randomly putting things in
a boxyou've got to arrange them in an orderly
fashion like oranges in an orange box. Anyway, we
immediately realized that, so we started out with a
configuration, a solid like order configuration, and
then jiggled the particles according to the pulse rate
distribution. And that is, in fact, known now as the
Monte Carlo Methodit was presumably
independently developed at Los Alamos by Teller,
Metropolis, and Rosenbluth. They actually got all the
credit. My guess is we did it first at Cal Tech. It's not
that difficult to come up with that algorithm, which,
by the way, I think is one of, if not THE, most
GAM: It still is, yes.
BA: The most powerful ever developed on computers, because you
need computers just to do this enormous amount of
juggling in the box; you can't do that by any other
mathematical or analytical technique, and for the first
time really solves numerically what is called the Many
Anyway, we juggled these particles and
realized that on this mechanical IBM computer we
couldn't go very far. Then Stan Frankel actually went
to England, to Manchester, where they had a
FERRANTI Machine. Which may have well been the
first electronic computer.
GAM: Can you give us a date on that?
BA: My guess it's the summer of 1950 that he went over. I was still
working on my Ph.D. thesis. He was really well known in computing circles.
He actually put the Monte Carlo Method on the
FERRANTI Computer and ran it all summer. I think it
was before Los Alamos had electronic computers
available. Anyway, we ran it and he came back. The
thing that happens, Kirkwood did not believe in my
boss, my thesis supervisor, he didn't believe in him at
the college and, of course, he had communication with
Los Alamos. The fact is, we never publishedyou can't
publish something your boss doesn't believe in! In the
meantime, Teller, Rosenbluth and Metropolis
independently published. There may have been some
collusion or communication of ideas that I couldn't
recall, but they had the machines, so they published
and we published only years later. There is, in fact, a
footnote in the Metropolis paper giving us credit of
having independently developed it. That got me a
connection with Edward Teller and when he came to
Cal Tech, he persuaded me to become a consultant. At
that time, after I finished at Cal Tech, I became what
was then called a Wrakov instructor which each
professor started out with at Berkeley. I think Teller
was at Berkeley when Livermore was foundedin
1952, I guess.
BA: I think I was almost immediately a consultant primarily because
I knew Teller, and I was used primarily to help with
the equations of state. I was probably the only man to
devise the equations of state in the early history of
weapons development at Livermore.
Also, this gets beside the point, I helped establish the
explosives station at site 300. I worked with that, but
that was an experimental phase of my career, I don't
think you would want to pursue that.
Then an interesting question came up which, in a physics sense,
was the 64 dollar question, whether hard spheres had a
phase transition. It turned out that the Los Alamos
people failed to find it, for some reason that I didn't
understand. We had predicted there would be oneit
stood ultimately on shaky ground but, nevertheless, I
believe it was something that had to be cleanly settled
in the Monte Carlo Method. They failed to see it.
What happened to me, I taught for three
years at Berkeley in Chemistry, then
took a Guggenheim abroad. When I came back, I
worked part time at Berkeley and part time at
Livermore, and eventually the computers, as you said
earlier, dragged me to Livermore and I gave up the
But the hard spheres business still bugged me and, so
I thought, well there's another way to try to see
whether the hard spheres have a phase transition and
that is to develop molecular dynamics, which has
since become a competitive and extremely powerful
methodology. Also, we solved the POSTUM many-body
problems, but the molecular dynamics can also
solve the time-dependent or transfer problem. Then, I
got Tom Wainwright whose office was down the hall
from me, interested in these questions, and I said I
needed somebody to talk to and work with, and he
became very interested. We actually developed, in
relatively short order, molecular dynamics.
GAM: Yes, I remember.
BA: It's sort of interesting that people predicted, I think including
Teller, that molecular dynamics would never be
competitive computationally with Monte Carlo
because it was so much more complicated. But it
turns out, when you finally get down to doing it, it's
very competitive. I guess that must have been about
1955 or 1956.
GAM: Well, as background in a sense, I remember Edward Teller
saying, at one of the LMG meetings, that we're now
through with this testing thing, so let's get to do some
physics with these machines and you and Tom came
up with your molecular dynamics scheme. I
remember Chuck Leith came up with the business of
simulating neurons and a few other things like that.
BA: Right, Project Moron, right. At one point Chuck and I...I guess it
was the LARC, or was it the UNIVAC?
GAM: The UNIVAC and then the 704 and then the LARC. The LARC
didn't show up until about 1960 or so.
BA: OK, I remember only Chuck and I competing for machine time.
But it was a very friendly competition. Anyway, we
developed molecular dynamics and that really swept
GAM: Well, your method was a really important thing all over the
BA: Oh yes, there isn't a university department that doesn't do both
Monte Carlo and molecular dynamics.
We then went back and reinvestigated the hard-sphere phase
transition. We found, actually, beautiful pictures of
solids in equilibrium with liquids,
GAM: Yes, I remember those pictures.
BA: Which, I think, got on many covers of freshmen textbooks and
into Scientific American, it really swept the field.
Then the Monte Carlo people, particularly Bill Wood
of Los Alamos, went back and redid more carefully
my Monte Carlo methods, and found the hard-sphere phase transition.
GAM: I remember back in 1958, during the Hardtack Phase I test series
in the Pacific, you sent out stuff to me there and I ran
hundreds of hours of STEP calculations out there.
BA: I remember that and I am very thankful to you for that, George.
We needed a lot of statistics because this liquid-solid
phase transition is a very rare event. It's very hard to
do that and machine time was THE important thing
at that point, to get a large amount of statistics. We
did two things, we taught all our friends and buddies
to help us run and we also developed an agreement
with Sid, which I think became very important too,
and that was to utilize the machines in a maximum
way to compute. Whenever there was an idle moment
we had an algorithm where we could just get in there,
whenever the scheduled computation couldn't run.
We fixed our programs so that they were ready to run
in an instant. In this way, we could get a few seconds
or whatever, that would otherwise have been unused,
So, we started to help other people to do the same
thing to utilize the computers really fully.
GAM: It used to annoy the A Division people, even though they
couldn't use the time, they didn't like it that you were
getting so much time. Actually though, their design
codes were very complicated especially compared to
your Molecular Dynamics program, and it always
took extra time to get them started.
BA: Right, but they got clever over the years too, and started doing
similar things to try to utilize all their time. But early
on, it helped Sid Fernbach to acquire more machines,
because even though people didn't know what the
machines were being used for he said, "Look, they are
being 99 odd per cent utilized, we need more
machines". In that political sense, it was very
important. We managed to abscond with a fair
number of machine cycles. Anyway, we settled the
GAM: Well, wasn't it sort of an unusual thing to build in, this
hard-sphere thing had a model, though, for potential wells
so you could model the sphere, at least, from the
potential point of view as inelastic.
BA: Well, would you deal with soft spheres or...
GAM: With soggy spheres?
BA: Soggy spheres, yes. I mean of course, that's sort of historically
interesting. We stuck to hard spheres because they are
several orders of magnitude faster than if you do the
same thing for soggy spheres and sticky spheres.
Because machine time was so valuable, for hard
spheres you can solve the collision dynamics
algebraically, rather than as a differential equation.
And that gives enough of an advantage numerically. And, it
turns out ultimately, it was in fact the key problem,
because it has all the essential physics in it and from a
theoretical point of view it's a much easier thing to
deal with as well as numerically.
GAM: I remember the stir of excitement that ran around the Lab when
you were talking about simulating boiling too.
BA: Right, right, now for boiling you do need the sticky, soft spheres.
We put on a square well and we saw the gas liquid
interface. That also got into a lot of pictures. Those
pictures may have well been the earliest graphics
examples of use.
GAM: Not quite, but they were certainly early, I made thousands of
feet of films for you and that guy in Berkeley.
BA: You helped us a lot, yes.
GAM: It was fun, I remember that.
BA: Yes, that guy in Berkeley, you know that's sort of interesting,
this was the Berkeley Physics series. You know there
was a Harvard-Berkeley Project at one time to
rewrite the freshmen physics text. Fred Rife, who was
the Berkeley guy if you recall was, in fact, heavily
involved in the statistical mechanical section of that
freshmen physics series. And he asked me, and with
your help, I succeeded in making some pictures.
The thing that was sort of interesting there, and is still
being used, let me explain that to you, is this problem
of irreversibility. Freshmen have a very difficult time
understanding the concept of irreversibility. The
point was, if you remember this, you had a box to be
divided into two and, in the first demonstration, we
had four particles in the left side and none in the right
hand side. And you run the system, and then you run
it backwards, and you can't tell what irreversible is.
When you run it forwards, and run it equal time
backwards, the four spheres end up being on the same
sides again, but it's not an unusual event because it's
a natural fluctuation. But, if you put a hundred
particles in, and you run it on half the size and half the
size of the box and none on the other. You run it
forward, it mixes, of course, all up and then you run it
backward and a hundred particles end back up in the
left hand side, of course, because the equation is
motion reversible. But, then everybody laughs,
because you recognize it's a terribly unusual event
with a hundred particles. So that got on the cover of
the freshman physics book. We tried something that
was a film loop that demonstrated just the thing I was
talking about dynamically. They were trying to sell
that loop with the book. I don't think it was a
commercial success, but it was used a lot. Many
fashionable physics professors have told me they
have used that demonstration to teach the concept of
GAM: There were lots of similar things like that going on through the
Commission on College Physics.
BA: Yes, that's right, I'd forgotten the auspices of this however. But
that service became very well used.
GAM: Well, yes, it was great stuff, it was very good use of the
BA: I agree. Graphics were very primitive in those days, and we
needed helpful people like you to make the thing go. I
think we spent about three months just getting these
film demonstrations working.
GAM: Yes, well things have gotten much better now, but it was more
BA: We only had black and white then, now they have color and
sound. Anyway, that was sort of interesting, this
whole hard spheres transition. Using the computers
for education purposes was extremely important and
selling it to the academic community a worthy task.
GAM: Along the way, we sort of covered the first fifteen or twenty
years of the Computation Department, but how close
did you work with Sid making decisions here, there,
or elsewhere? You were an advisor to him, weren't
BA: Yes. The things that we did that ultimately turned
out to be very important. We founded the Methods of
Computational Physics, the book series. I had a friend
in the publishing business and we were chatting one
day about all this material developed at Los Alamos
and Lawrence Livermore on hydrodynamic
phenomena, and that we should publish it and get more
people in the academic world to participate. So we
started that. There was a huge problem about
declassifying all this material, but we brought out
close to twenty volumes. Each book dedicated to a
specific field, such as statistical mechanics, quantum
mechanics, fluid dynamics, solid state, and that was
the early, extremely important project of getting more
people involved in the field. Sid used all his friends, I
did a lot of the legwork, but I used to run into him
and ask, "How do we get this going"? and so forth.
Then we started the journal Computation, which is still a key
GAM: Yes, it is a very good journal.
BA: Because we realized the books took several years to produce
and we needed a quicker communication means.
GAM: I still have some of those journals. They are still the best
treatment for that early stuff, very good stuff.
BA: The journal still has, even today, the key articles, the key
At the end of Sid's career, speaking of publications and so on, he
sort of had the idea of starting a division within the Physical
Society. You know, they have the Energy
Division, the Plasma Division, Materials Division. So
we had a Computation Physics Division. He, at that
point, was no longer associated with the Laboratory,
but we met occasionally, and he had a desire to do
that, so I really worked at it and helped him get that
going. We went to the American Physical Society for
support. It's a very successful Division, and it became
a Division almost immediately. We got some 2000
members without even trying.
GAM: So after this journal got started, I remember seeing all over the
world references to the Fernbach, Alder things, OK?
As I said, I have some in my own library that I think
are great. The best treatment for the initial ideas of
hydrodynamics and things like that that I've ever
seen. But I was thinking more in the sense of dealing
with Sid. Yes, I know you guys pioneered this
business of publishing the Computational Books too,
which were very good. But I was thinking more of the
day to day like when you were going to work out
some strategy for getting a new machine or work out
some strategy for equitably sharing the time available
on the computers. Were you involved in any of that?
BA: No, he did the acquisition of the computers, I never did any of
that. I always wanted the biggest and the best, but I
really couldn't help him with that.
For example, the use of the spare cycles was an issue that we felt
very strongly about and he pushed it. I'd say, "Why
don't we do that?" and he implemented it. He'd get
people to agree, not only in the Lab, but also outside
the Lab. That was a big problem.
GAM: That seems so obvious!
BA: Yes, but people wouldn't initially agree.
GAM: It's just a dog in the manger act..
BA: Well, you know what the people in the Lab say: "You're cutting
into our time this way", and then we'd show that
swapping information each way was trivial in terms
of time used. But there were also intellectual
considerations, where you couldn't let outsiders use a
government machine that was dedicated to weapons.
Machine time was really a valuable commodity in
those days. To use it for this whole equation of state
business was based on the development of Monte
Carlo. Anyway, I remember he had a hard time
getting agreement both inside and outside the
Our communication was extremely informal, I ran into his office,
or he looked me up, or we met in the hall, or we had
lunch, or just chatted. It was never formal; we
respected each other. He was always interested in
developing new ideas and encouraging more use and
intelligent use of computers. But I took the sort of
intellectual end and he took the more administrative,
practical, and political ends. He was very good at
that. We had lots of fun trying new things.
GAM: I don't know if it was the Laboratory or Sid, but you had some
excellent support in MaryAnn Mansigh, who was
devoted to your project all the time. And, I remember,
Norman made some interesting contributions about
developing a neighborhood concept that made STEP
run much faster.
BA: That's right, in those days, people like me didn't really program.
That was dirty work and, even then, very time
consuming. So, I worked through a programmer.
MaryAnn Mansigh was my loyal twenty-odd year
programmer. I tried to get her to be more innovative,
but she preferred to stick with a very conservative
GAM: She did what you wanted her to do.
BA: She did exactly. Nowadays, that is no longer practical. Now, you
have Physicists with PhDs who are trained in the
computing business, but that just wasn't available
then. And, if you do more sophisticated computing,
you need people who know both programming and
For example, we spoke to Norman about speeding up the hard
sphere algorithm, the molecular dynamics algorithm,
and you don't have to search the whole system for the
next collision, you just need to know the domain.
Intellectually, it's not a very difficult thing, you just
need a neighborhood or domain decomposition,
whatever fancy name they have now, but it's
GAM: It was innovative at the time.
BA: Yes, but in retrospect, nothing was really difficult. That's, of
course, the beauty of being a pioneer in the field. Do
the easy thingsget the cream off the top. It took
Norm quite a few months. He had other things to do,
but he actually coded the nearest neighbor algorithm,
and this speeded the thing up.
GAM: Yes, I remember him on it. He was my office mate.
BA: He is a brilliant guy.
GAM: Indeed, he is.
BA: He wasn't assigned to do this, he was just interested. We were
all interested in doing this stuff, no formal
arrangementswe just did it. It was an extremely
The interesting thing is that neither the Monte Carlo algorithm
nor the Molecular Dynamics algorithm have
significantly changed since their inception. Once we
made these, what we think now are, obvious
improvements, basically, people are still using them.
Monte Carlo, of course, is easily parallelizable, which
we couldn't do in these days with Molecular
Dynamicswhich can't be made parallel even when
people think they can. But, basically, the arguments are
unchanged. The original algorithm is still valid. When
people first build something it's not always the most
GAM: Well, that's true.
BA: It turns out, we build an algorithm that is close, I have not seen
any significant changes.
GAM: Just apropos, if nothing else, is anything of this stuff being
carried on today?
BA: You mean the Monte Carlo or Molecular Dynamics?
GAM: Yes, that you were involved with at the Lab.
BA: Oh yes.
GAM: How about Jim Belac, I was always impressed with the stuff that
he was doing.
BA: There are a number of people who are trying to build Molecular
Dynamics into bigger and bigger systems. We were
stuck in the early days because we only had
memories of a hundred words. We could do, maybe, a
hundred particles at most. Well, they can now do ten
million particles, and Belac is one of those people who
just, by brute force, does bigger systems. Runs them
maybe longer, on much more capable computers, but
that's not my cup of tea.
There are some very recent developments that we are trying to
work, and which we may want to briefly discuss. One
of the problems, is it's computationally very
expensive to run fluid dynamics compared, of course,
to Navier Stokes, right? And people are trying to
bridge this gap between Molecular Dynamics, the
Particle Method and the Continuum Method. The
Particle Method you can't run more than 8 seconds
and maybe run 10 to the 6th or 10 to the 7th particles. But
that's not going to get you to turbulence or whatever.
So, our most recent ideas for extending Molecular
Dynamics is to do what is called "Imbedding".
Imbedding a particle method into the continuum. So
only, for example, where you need detailed particle
informationit's sort of an adaptive algorithm;
within an adaptive gridding. That may extend
Molecular Dynamics by many orders of magnitude.
That's our latest idea that works very well with
parallel machines. It's amazing that people have not
done that actually. But that's a relatively recent thing
still to be done.
GAM: I think it's amazing that people have not done a lot of things
and I must admit I don't know why. Some things are
hard to do, I suppose.
This thing you are talking about with adaptive gridding and so
forth, I worked with some aspect of it with Garry
Rodrigue. He was busy trying to put it on a sound
BA: There's this group of people with Phil Colella and John Bell, I'm
not quite sure they fit into your time history, but I
brought them to the Lab and they are the ones who
really made adaptive gridding work. And it is highly
successful, but that's within Navier Stokes. One puts
the gridding where the action is basically. The latest
thing we are talking about is extending that when the
gridding gets very fine, very small scale, then you put
in a particle algorithm instead of the diffusion
method. That's very successful.
GAM: And you are carrying that on now both at the Laboratory and at
BA: Yes, well, one of the groups, the Bell, Colella group has left to go
to LBL and we are working with them as well as a
newer group here at the Lab under Steve Ashby.
We're trying to work with this group to try to do the
same adaptive gridding and imbedding algorithms.
GAM: Yes, I've heard of them.
BA: The other thing that is a significant development in the
extension of Monte Carlo Methods, which I've
personally been involved with at the Lab with a man
named David Seperly, is solving the quantum many
body problem. Solving the Schroedinger equation by
Monte Carlo method which has been a pioneering
effort also. I think we did a superb job on that. It has
its technical difficulties with the Fermion problem,
which is one of the deep instability problems in
numerical algorithms, which has not yet been
GAM: Where is David now?
BA: David is a Professor at the University of Illinois. The key thing
we did there, which is one of the key papers that has
been published in Condensed Matter was the uniform
electron gas, the jellion. That turns out to be a most
cited paper, or was, at least, a few years ago, in
Condensed Matter. That was sort of interesting. There
were three papers written up of ours, or mine, in the
hundred-year anniversary issue of The American
Physical Society. They published significant papers in
this issue and they picked three of ours. One was the
hard spheres transition; one was the discovery of the
long time tail in the auto correlation function, which
completely overthrew the existing kinetic theory. The
fact that there was a long-term memory and not a
Markov process involved. And the third was this
condensed matter thing. All these were developed at
the lab where all those marvelous computers are held.
GAM: Beyond that, the computers are there, but so are the people who
have the skill to use them.
BA: Yes, you need an idea. You see the problem is you can do
intellectually interesting things on the computer
instead of just engineering things. You can do really
innovative discoveries and that's my bag trying to use
the computers to gain more insight into Physics.
GAM: That's what it's really for.
BA: I think so. Well, that's what it's usually for, it's now used for
sending e-mail back and forth.
GAM: Something here about reverse evolution?
BA: Right, it's astounding what computers are being used for, let me
go back to one other thing that is sort of interesting,
my admiration for Stan Frankel at Cal Tech, who
worked at Los Alamos during the war and then came
to Cal Tech. Very few people know of him because he
never got tenure at Cal Tech and then went off to
some oil company as a consultant.
But in 1949 or 1950 he was most interested in building a personal
computer. He was fiddling in his lab trying to build a
small personal computer.
GAM: It was virtually impossible then, the components didn't exist.
BA: That's right, he didn't have a semi conductor. But his idea was
way ahead of its time.
GAM: It would be nice to have more of a detailed description of that
for others to read later on.
BA: You should get a hold of Stan Frankel. I lost track of him after
we wrote our paper on the Monte Carlo Method with
him which was published in the middle 1950s, a year
or two after Teller and Rosenblum's paper. I've lost
track. I know he was at some oil company.
GAM: Speaking of Teller, were there any of your interactions with him
that you can remember?
BA: Well, we certainly talked a lot in the early days of our mutual
interest of the Monte Carlo Method and molecular
dynamics. I was very much in favor of starting the
Department of Applied Science at Livermore of which
I am one of the founding members. Edward and I
worked together in that. Neither of us stuck there
very long, it was sort of awkward.
GAM: The one person I heard who was against it was Emilio Segre.
BA: It's very complicated, I don't want to get into that, it's a physics
thing. Berkeley physics was opposed and then it got
into Davis and Davis physics opposed it. It was the
political connection of the university with a weapons
lab, and ultimately it ended up in the sort of awkward
Engineering Division. They forced it down their
throat, and it's been a sort of stepchild of Livermore
and a stepchild of Davis. I'm still involved with the
Department of Applied Science. I ultimately went
back to it. They wanted me to come back and help
them organize it. I was on a bunch of committees and
now that I am retired, I occasionally help them with
advice. That department is being reexamined. The
idea was to use the Laboratory as a training ground
because it had unique equipment such as the
computers, the high explosive facility, and lasers to
get students trained in the advanced and
multi-disciplinary research. It has worked to some extent,
but not nearly as well as I think it should.
GAM: Well, maybe after the smoke had cleared, the degree of
cooperation that one extracted from the various parts
wasn't all that hot. I remember I taught out at DAS for
a bit and I was told that that's on me, it did me no
good at the Lab.
BA: It was funny, the Lab supported, in principle, education.
GAM: Yes, but only in principle.
BA: The hierarchy did, but when it came to the nitty-gritty people,
they wouldn't do it. So it changed that.
GAM: So, it worked out a little bit. And I will tell you in the computing
area, there have been some very, very, talented people
that got produced at DAS.
BA: And it turns out, that half the graduate students still want to go
into computational physics. But the staff at this point
is very low. I'm trying to remedy that in my retired
status. Teller has never really spent enough time out
there to make it flourish. Even in the old days, my
guess is it got so politically complicated at the end
that he didn't want to deal with the Davis section and
just sort of gave up.
GAM: Back to a semi-technical question. One of the things that seems
to be a great concern in the Monte Carlo Method is its
spread across an arbitrary number of processors. How
do you keep the seed from being inbred or being
repeated over and over again?
BA: Are you talking about random number generators?
BA: They now have random number generators that they can test.
You see, because the machines have gotten so big
there's a danger that the random number generator
has a periodicity. They now have tests that know how
long it takes for random number generators to repeat
or to get back to the same initial state.
GAM: But, from the technical, or philosophical, point of view, it's
obvious that that's got to be avoided if you intend to
BA: Oh, by all means, and you can test that very simply by
generating random numbers and just plot them. And
use the generator to see whether the area you are
trying to cover is uniformly covered. Whether you
have stripes or empty regions.
GAM: I remember doing that many times and seeing holes in the
BA: Then you know you have a problem, right? Exactly! That's a
highly technical thing. Actually, Chuck Leith got
involved in that.
GAM: Oh, really, I didn't know that?
BA: I just ran across that. He published a paper in our Journal of
Computational Physics with some woman who is not
at Livermore on the Randomness of Other Memory
Generators and trying to make sure that they are
random over these many more samples. But there are
GAM: But you are telling me that people recognize that there is a
problem and they're doing something about it?
BA: Right, and massively parallel computers force you into that
because the numbers are used so many more times
and you need so many more different runs.
GAM: Well, I think it's rather germane to the question in these ASCI
computers that they are trying to foist off on the
scientific community right now.
BA: Right. Oh yeah, we are planning to use the ASCIs, the blue
machine one of these days.
GAM: It's fine to use it, you know, if you could leave the politics out of
it, and the hype, I think it's likely it could answer
some interesting physical questions and it would be
worth it. Many of those questions are the same ones
that we talked about thirty years ago and you
couldn't do it then because you didn't have the
BA: Right, you couldn't solve them very fast. You must have a
perspective, I personally think you know, people get
all excited about a computer that has a power of 10 or
a 100 times more powerful than the one they have. But
the problems that you need to solve are almost so
complex that even that factor is not very important.
So, not only do you want bigger machines, you have
to be clever about usage, if you can. For example,
turbulence or three-dimensional hydrodynamics,
those are problems that can eat up an arbitrary
capacity on any computer we're ever likely to see. So
you have to be clever.
GAM: Well, Great, can you think of anything else that you'd like to
add before we turn this thing off?
BA: Well, have we answered all the questions?
GAM: Well, it's not the questions so much, it jogs your memory, OK? I
think you've covered everything you wanted to say
here, and I want to thank you for taking the time to
revisit this memory lane.
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