The size of the group is currently back to its minimum value:
Professor Judah Schwartz returned to MIT in August after a very useful visit. David Ralphs finished his Sandwich at the Laboratory and is now back at Brunel University. It is quite likely that he will return next summer for a second period. The group's size should increase next quarter with the arrival of D C Toll (DCT) and A H Francis (AHF). In addition a sandwich student, David Sedar, will be with the group until February.
We now have all the hardware! The PDP15 was moved into the new building at the end of July with very little trouble. The move took place over a weekend and it was up and working again by Monday morning. Soon after this the extra 16k of core storage and disc arrived. Unfortunately due to shortage of DEC engineers through holidays and illness, we were unable to get the equipment attached until the beginning of September. In the meantime the replacement graphics hardware arrived and also the writing tablet. These have all been installed and are working correctly apart from the graphics hardware. The equipment now consists of:-
We have still not accepted the graphics hardware although the new arbitrary vector hardware is considerably better than the basic hardware we had before. This was only capable of drawing in 8 basic directions whereas the new hardware can produce lines in any direction and of any length. A number of faults we had with the old hardware have disappeared leaving one or two still remaining. The accuracy of the arbitrary direction is still not good enough. The vectors overshoot by a sufficient amount to make it difficult to view a picture with a number of closely packed lines. However, the vectors in the 8 basic directions are reasonably accurate and we feel the arbitrary vectors are probably just a matter of improving the setup. A more annoying fault is that we are getting crosstalk between the input/output devices and the display. Transfers to DEC tape, disc and magnetic tape cause the display screen to flicker and produce spurious output. Occasionally the display vanishes completely and only returns with the next initialisation of the display file.
The writing tablet provides us with a useful alternative to the lightpen. It works basically by generating a spark from the pen tip which is heard at the edges of the tablet. Calculating the difference in time between spark and sound and knowing velocities of light and sound gives you the position of the pen on the display. The repeatability and accuracy of the device is good. It can work in two different modes. Either sparks are produced at regular intervals or alternatively a single spark is produced when the pen is pressed down.
As indicated above, considerable time has been lost on the display this quarter due to installation and fault detection and correction.
We have had yet another bad quarter with the SD4020. The high intensity on the tube necessary for the new paper has meant that the engineer has had considerable difficulty in getting long and short vectors matched in intensity. In addition a number of faults on the old tube finally caused us to introduce the replacement tube. This also exhibited hardware faults. Eventually a new tube was obtained from San Diego but, unfortunately, the intensity of the new tube was so bad that we were forced to go back to using the original one. We now have a resident engineer which should improve the maintenance of the machine. In addition a new tube and the new cine camera should arrive in the next quarter which, we hope, will cure most of the faults. The old 16mm camera has been exhibiting considerable jitter just lately.
During the next quarter, the Operations Group will be introducing three-shift working on the SD4020 and this should significantly increase the turnround which has been particularly bad recently due partly to build up of work and also the large amount of downtime on the SD4020.
The introduction of the disc into the system has caused a considerable amount of rethinking how we use the PDP15. The disc is equivalent to about 1 2/3 DEC tapes and is used to contain the Monitor tape and a Scratch tape. User files are still kept on DEC tape, being moved to the disc before starting a session and returning them to DEC tape at the end.
The CONTROL X monitor system provided by DEC now works (it would never work from DEC tape for some unknown reason!). It is now possible to divert all output usually destined for the teletype to the display. Listing and editing of files is considerably speeded up by this.
The writing tablet arrived without a handler. GAE has written one for it called VWA. Full details will be given in a SPROGS paper to be published shortly.
Once the new display hardware was installed, we unfortunately found that all our display programs stopped working. The standard DEC software checks whether the arbitrary vector option is available and generates orders accordingly. However the orders generated by the software were completely different from those expected by the hardware. JRG has made the necessary patches and we now have a working system once more. The size of display files has decreased significantly.
A program to read SD4020 tapes and display selected frames on the VT15 became available in a pilot form in August. It has already proved useful in reducing the time necessary to produce a film sequence by circumventing the bottleneck caused by the turnround of hardcopy runs on the SD4020. It is particularly useful at times when the SD4020 is out of action.
A user can select a frame by number from the keyboard. The program scans through the tape counting the frames until the selected frame is found and then displays it. Since each frame is translated into display orders as it is scanned, a crude movie effect is obtained as the program moves down the tape.
Experience gained by having several people use the program has brought to light ideas for improvement. Those that are simple to implement will be introduced shortly.
The ability to edit a tape and the ability to speed up the movie effect (at present a maximum of 2 frames per second) will be considered in a future edition of the program. Speed will undoubtedly be increased by using the disc to save an intermediate form of the movie sequence.
The program for defining character fonts on the PDP 15 is now complete. An additional program is nearly ready which allows a user to generate slides of textual information on the SD4020. When finished this should provide a useful facility for laboratory staff. A few bugs still remain and, now we have the additional core, the various parts will be combined into a single program. It is also likely that use of the lightpen will be replaced by the writing tablet in the font definition.
The POLYGRAPHICS system is now working on the 360/75 at the Rutherford Laboratory. However, due to the size of core required, it is only run overnight and consequently turnround is very poor. It is hoped that the program can be modified to run in an overlaid structure to keep the core requirements lower. It should then be possible to get a 6 hour turnround. There seems little chance of getting this package within the restrictions of the express queue.
Once we have obtained clearance from the originators, a local manual for the system will be produced.
The Atlas version of the system was issued in July and already has a number of users. The PDP15 version of CAMP appears to be working apart from one major undiscovered bug. With the additional core store and disc backing, it should be possible to generate complete films using the PDP15. It will be interesting to get a comparison of the times on Atlas and the PDP15. CAMPER has been loaded onto the PDP15 but requires considerable work before it will be useable.
Progress in the last quarter has been minimal due to pressure of work from other sides. A number of inconsistencies in the draft proposal (SPROGS No.8) have been realised and a revised draft of the basic system is being developed.
A film sequence of Aerial Synthesis is nearing the production stage. This shows positions of aerials on the earth's surface. This has been requested by the Department of Education and Science for an exhibition of the work of the Research Councils in the London Science Museum from May to October 1972.
A film showing the effect of different speeds of chemical reactions in a process of the form A+B+C was defined by Peter Groves of the University of Aston. FRAH spent a couple of weeks debugging the film in order to get it completed in time for the Visual Media in Chemistry Conference. One quite visual sequence shows the analogy between the chemical reaction and a water system consisting of three tanks. The speed of the chemical reaction is analogous to the degree that the taps between the tanks are open.
Judah Schwartz completed one film during his stay which complements the Schrodinger film produced by FRAH for the Nuffield Foundation. Full details are given below:-
Students are now encountering quantum mechanics very much earlier in the course of their education than was common a decade or so ago, and consequently one frequently finds that ones students are not as comfortable with eigenvalue problems as one might hope. The purpose of this paper is to describe a film made to offer a different perspective on a standard eigenvalue problem, ie the bound states of a square well.
There are several films now available that plot the wave function as a function of distance for successive values at a trial eigenvalue. If the boundary condition at the origin is satisfied, then one sees the exponential growth of the solution to the Schrodinger equation at large distances when the trial eigenvalue does not correspond to one of the allowed energies of the system. In the linear superposition of exponentials that is the solution the coefficient of the growing exponential term goes through zero as the eigenvalue is passed. This presentation gives a vivid feeling for the behaviour of the solutions to the differential equation.
Because this sort of problem is in all likelihood new to the student, it is worth considering alternative presentations that may tend to emphasize other aspects of the problem. One such presentation and the one we have chosen to depict in a film, is the presentation of the phase plane in which the solution is plotted against its spatial derivative. A description of the film follows.
The reduced radial wave equation with zero angular momentum (or the one, dimensional square well with odd parity wave functions) is:
-d2y / dx2 + V(x) u = Eu
where
V(x) = -V0 when x ≤ a
V(x) = 0 when x > a
and h = 2m = 1
A straightforward calculation indicates that for x < a the trajectory in the u, du/dx plane is elliptical and that for x > a the solution u(x) is such that u(x) approaches esqrt(Ex) as x approaches infinity when E is not one of the eigenvalues of the system.
Since in this region the derivative is proportional to the function the trajectory in the phase plane is a straight line whose slope is governed by the trial eigenvalue. If the trial eigenvalue is one of the allowed energies of the system the trajectory asymptotically approaches the origin.
For this film we chose a=π and V0=30.
In the first scene, the differential equation is integrated numerically with a trial eigenvalue and the trajectory in the phase plane is traced out. This process is repeated several times as the trial eigenvalue is changed in an attempt to converge on one of the eigenvalues of the well. In watching this sequence a student should be able to tell on which side of the real eigenvalue the trial eigenvalue is and also to be able to account for the varying rate at which the trajectory is traced out. Further the student should be able to describe how to deduce the trial eigenvalue from the asymptotic slope of the phase plane trajectory in the units of the plot and be able to describe qualitatively how this scene would differ if even functions were being generated rather than odd ones.
In the second scene, the trial eigenvalue is changed smoothly from -V0 ≤ E ≤ 0 and the resulting trajectories shown. An energy scale keeps track of the value of E and a mark is made on the scale each time an eigenvalue is passed. Since the initial value of the slope is the same for each value of E, the elliptical portion of the trajectory gets smaller as the trial energy increases. The student should be able to explain this fact and be able to discuss the problem of normalizing the eigenstates. If these trajectories are interpreted as being appropriate to the odd solutions to the Schrodinger equation in one dimension, the student should be able to discuss the possible number of bound states of even as well as odd parity.
In the final scene the value of E is set to zero and the well depth is varied so that -30 ≤ V0 ≤ 0 and the resulting trajectories shown as V0 varies smoothly. The student should be able to account for all the features of any trajectory in a qualitative way as well as be able to make inferences about the number of bound states such a well could support.
This problem is a simple one. It is analytically soluble. Perhaps for these very reasons it is useful to look at it from a quite different point of view. The author will consider himself well rewarded if some students do so with relish and are led to re-examine other things they already know.
The Stage 1 report has been issued which lists equipment and facilities available at ACL, RHEL, Harwell, Culham and Oxford Polytechnic;. A questionnaire circulated around the. Laboratory attempted to determine the use of equipment currently available and facilities still required.
The organisation of the Symposium took up most of PMN's time during July. It was held in the Rutherford Laboratory Lecture Theatre on 30 July. The event lasted from 10.30 am to 8.00 pm and proved highly successful. It was attended by 150 people. A repeat of the film portion of the Symposium drew over 100 people the following week. A questionnaire, sent out with a transcript of the Question Session, was returned by about 60 participants. A summary of the opinions expressed will be included in a later report. Considerable credit must go to PMN, DAP and the Rutherford and Atlas staff involved for the professional way it was organised. The Symposium was, on the whole, favourably reviewed in the press. Two examples, out of context of course:
It was also one of the best organised meetings that has been attended recently running very close to the scheduled timing and with a standard of presentation of a very high order for once the visual aids were well handled, part of the proceedings and not a makeshift addendum to them. One might well add 'Others please copy FILM USER Sept 1971
The subject of computer animation flared into prominence in the last fortnight when a one-day symposium was held by the Science Research Council at the Atlas Computer Laboratory in Didcot. This seems to be the spiritual home of the craft in Britain Financial Times 10 Aug 1971
In July we were approached by the BBC's Tomorrow's World programme for help in producing a sequence on Computers and the Animation Industry. The aim was to show how a computer could be used to aid the professional animator in the design stage of his work.
To show how the D-MAC pencil follower and display could be used to check out an animation sequence, JRG produced the following system:-
In July, the limited size of the core storage and absence of arbitrary vectors meant that we were unable to get the display changing in real time and only managed to change the quite complex display at 3 frames a second.
It was to some extent unfortunate that the programme had to be produced in July. Using the writing tablet as input and the disc for storing both the individual pictures and the display sequence, a much improved speed could have been achieved.
To show how the same cat and dog input could be used to produce a film on the SD4020, GAE digitised the pictures C1 to C6 and B1 to B4 using the D-MAC package and generated the required film on the SD4020. In addition various effects involving the cat and dog were produced showing how such drawings could be manipulated easily by computer.
Finally the BBC wished to show how the computer could be used to generate in-between frames automatically. An animation usually consists of a set of key frames which are produced initially. At a later date the frames required in-between the major frames are generated. In order to get the timing correct it is important that the correct number of in-betweens are specified.
FRAH digitised the six major frames of a man walking. Standard GROATS software was used to generate a number of different sets of in-between frames showing how the computer could be used very simply to vary the timing of the sequence.
The BBC programme was televised in September.
It is hoped that some use of the 1906A will be achieved in the next quarter. DCT will be moving GROATS to the 1906A and GAE will be working on the link software between the 1906A and the PDP15. AHF will be proceeding with the CAMP/CAMPER implementation on the PDP15. FRAH has a number of films which require completing and also continues with the redraft of the SPROGS system. JRG should be able to help in this work once the SD4020 tape viewer is completed.
G A England attended the IFIP 71 conference Ljubljana
J R Gallop attended the European DECUS meeting at Amsterdam
