I write, therefore I am
With this variation on a famous statement by the philosopher Descartes, I would like to express that writing about what happens in my life is important to me.
BooksAt 12:37, I bought the following two books from bookshop Broekhuis:
Wednesday, October 8, 2014
Avoiding mergingI already wrote about merging in distributed version control and the complex problem of conflict resolution in my series of postings about concurrency in modeling (as part of software enginering). When users are changing a model in close operation, pessimistic concurrency control it the obvious choice especially if you have many small objects with relatively little information which are easily created, deleted, split, joined and/or rearrange in a hierarchy. Many source code management make use of optimistic locking and have tool support for textual merging edits in source files. But here the number of objects (files) are small and most edit take place inside the objects without changing the hierarchy (directory structure). A disadvantage of pessimistic locking is that it requires access to a lock server. There is for example a problem with working off-line. This can be avoided by issueing lock before going off-line and simply restricting operations that do not match the locks.
In large scale modelling where groups of people are working in seperation on parts of the model, sometimes without knowing each other, and where parts of the model are combined in a different location, a centralized repository is often not the right solution, and pessimistic locking is not possible and merging seems to be required. But this is not the case. It is possible, and maybe even desirable, to avoid merging at all. In large scale modelling changes to parts of the model are not often exchanged but mostly released in a controlled process often including reviews. In these cases the model is divided in parts where mostly one group is working at a certain part of the model at the same time. This means that pessimistic locking can be applied on the level of parts of the model. But there is a hitch, it is very likely that there are many reference between objects in the various parts that might have some consistency requirements. It is important to realize that a relationship between two objects belong to different parts, must (as an object) also belong to some part, either one of the two different parts or to a third part. When a model is divided into parts, one has to decide where objects that reference objects from different parts should be housed. Dividing a model into parts along authorities (persons or organisations) who are responsible for maintaining them, fits very well with the fourth level of modelling of information systems.
When two parts of a model are released separately, it means that reference between objects (with a consistency constraint) cannot occur in both directions. At first this may seem an unwanted restriction, but also from a semantic point of view it makes sense. If two parts depend on each other (and changes to them are not released as a unit) it means that when a new release for the part being referenced is created, the other parts need to be updated and released again to create a consistent version of the whole model (even if no real changes to the objects in the part need to be made). It is possible to define which releases of all the parts form a consistent configuration.
It is very tempting to consider two consecutive releases of a part as a kind of revisions where objects are simply associated by means of an identifier. This line of thinking suggest that merging is simple and that global unique identifier of objects are central. But this is wrong because it is not possible on the basis of some kind of identifier (name, GUID, URI, IRI, and/or others) to determine if two objects in different versions are semantically the same, unless such an association has been formally defined. In effect one need to define a relationship between the objects of two releases to know how the changes should be applied in all other parts that reference this part. Such a releationship could be defined on the basis of a combination of identifiers, but in many cases, when objects are split and joined between releases, it is not possible to define a one-to-one relationship.
When creating a new release for a part for a new release of a part it depends on, it might be needed that for some time, the part contains references to both releases, to support the process where the references are updated one-by-one to the object in the new release. In many cases this could be an automatic process based on the association defined between the two releases, but for example, when an object is split, it might be that a choice need to made about to which of the two (or more) objects the reference need to be made to. This all may seem to be overly complicated, but I think it is best way to deal with the inherent problems of large scale modelling.
The Conspiracy agains the Human RaceThis morning I finished reading the book The Conspiracy against the Human Race by Thomas Ligotti, who is a contemporary American horror author and reclusive literary cult figure. Although this book is presented as non-fiction, while reading it, I often wonderd if it is might be just one of his best horror stories. The book is inspired by The Last messiah by Peter Wessel Zapffe, a rather obscure, pessimistic Norwegian philosopher, whoes central thought is that conciousness is a mistake of evolution and that therefore it would be best if we as humans would stop from getting children. This all stems from materialism which states that there is nothing beyond life and that death is simply the end. There are many good reasons that support materalism, but one can never be sure that ther eis indeed nothing outside the universe in which we live. Because the idea that your existendec ends with death seems to make everything utterly meaningless (or MALIGNANTLY USELESS, as Ligotti writes), many people believe that there must be something beyond the observable world. But if it is indeed the case that everything is just meaningless, and that it is also impossible to add some meaning to life, it can als be serve as a form of (stepping stone to) enlightment because it leaves the Now as anything there is. Ligotty does not talk about this from what he writes (including a quote from part VII of Confessions by Lev Nikolayevich Tolstoy) one can conclude that he views the 'state' of enlightmens as but one of the ways to live in denial of reality, to silence conscious realisation that life ends in death, that all life ends in death, that our whole universe will one day end of become totally 'frozen'.
I found some parts of th book difficult to read. The forword by Ray Brassier seems to be written with the help of a thesaurus to pick the most uncommon words and expressions.
Sunday, September 21, 2014
Wednesday, September 17, 2014
Monday, September 15, 2014
GOGBOTIn the morning, I visited TETEM art space and say Cycles by Joris Strijbos. I also looked at the other works, I only find Facing forces by Juuke Schoorl. In the afternoon, I visited several locations in the center of the city but due to time limits I was not able to see everything. This year there is a quit strong focus on visual aspects. I watched a laser projection by Ksenija Pankratova and Vladimir Grafov and PARSEC by Daan Johan and Joris Strijbos.
Water carrierAnnabel had to design a device to carry water using a square sheet of waterproof carton. Her design (as shown to the right) is made from a single piece and does not make use of duct tape. The design goal was that the device should be able to carry 3 liters of liquid. Her design has a volume of more than 11 liters. It can be carried on the head or Hier het ontwerp van Annabel voor een waterdrager gemaakt van een vierkante meter geplastificeerd karton. Haar ontwerp bestaat uit een stuk en maakt geen gebruik van plakband. Het idee was om een waterdrager uit goedkope materialen te maken die in bijvoorbeeld een vluchtelingenkamp ingezet zou kunnen worden. De waterdrager zou minimaal 3 liter moeten kunnen bevatten. Haar ontwerp heeft een volume van ruim 11 liter. Hij kan zowel op het hoofd als aan de hand gedragen worden. Vooral de handgrepen zijn slim ontworpen. De naar binnen stekende stukjes karton vormen een driehoek met de bovenranden wat het dragen comfortabel maakt en tevens voor extra stevigheid zorgt.
ChestnutAt 17:24, I found the chestnut shown on the right at the start of Jan Porcellisstraat coming from Andriaan van de Veldestraat (Street view). This is the first chestnut I saw this year. It seems pretty early. Maybe due to the fact that the past weeks have been relatively cold for the time of the year.
ScheltemaThis morning, I visited bookshop Scheltema in Amsterdam. I mostly looked around on the top floors with books on sale and second hand books. At 11:46, I purchased a black, hardback Moleskine Daily Diary / Planner of 2015 (ISBN:9788867322626) for € 16.90. Stedelijk Museum in Amsterdam. There I went to see the exhibition Bad Thoughts - Collection Martijn and Jeannette Sanders. It includes the work Computer Structuren 2, 1970-1971 by Peter Struycken. At the end of the afternoon, I went to the opening of the exhibition RGB exit with seventeen new works by Peter Struycken in the series 'Kleurverhouding' (colour relationships). Each work consists of two square paintings on canvas with the size 60 cm. The left one is painted according to a fixed pattern on a grid of six by six squares using six colours, such that every colour occurs exactly six times. The right one is painted on a five by five square where the colours occur at the ratios 1, 2, 3, 5, 6, and 8. The pattern used for each work is unique. The hues of the six colours are placed on fixed positions on the colour wheel that are evenly spaced. The saturation and the brightness are different for each work. The idea of this works is to show that the impact of saturation and brightness have a greater impact on the colour experience than the hue. I met Peter Struycken while he was talking with Carel Blotkamp. We only briefly talked. Many people talked with him. There was a lot of interest for his works. I did talk with Zsa-Zsa Eyck and agreed that in the future I should maybe investigate the works that they still have in stock. Maybe I am going to visit this exhibition again before it ends at October 18, just to have a quiet look at all the works as it might be the last time that they can be seen together.
Wednesday, September 3, 2014
Impatiens glanduliferaYesterday, I noticed some special flowers along the road, and I took the close-up picture on the right. I thought I had found some orchid, but when at home I tried to determine it, I could not find me. This morning, I asked some colleagues if they had some idea. One of them thought it was an impatiens. After some searching, I concluded that it might be an impatiens glandulifera. Someone on twitter affirmed this.
For the love of PhysicsAt 12:51:48, I bought the book For the love of Physics by Walter Lewin, ISBN:9781451607130, from bookshop Broekhuis for € 9.95 (second hand). Chapter 15 of the book, with the title Ways of Seeing talks about his friendship with Peter Struycken. Walter Lewin helped Peter Struycken by making some suggestions for mathematical formuleas that he could use for his computer art works. Many of his art works are based on these suggestions.
Thursday, August 14, 2014
Wednesday, August 13, 2014
Third visit to Peter StruyckenI visited Peter Struycken. Besides talking about all kinds of things, we also went throught the list of his works on the page I have made and reordered the works before 1969 based on his recollections about which works were made in the same periode. We also discovered that there are still some early works missing when we looked at some pictures that were taken during the openings of some early exhibitions. I also returned the part of his personal archive that I took with me last October and took some new part home.
Thursday, August 7, 2014
Triangulation of regular polygonsThe number of ways a regular polygon with n-2 sides can be dissected into triangles (also known as triangulation) is given by the Catalan number Cn. Every pair of triangulation for a given regular polygon has a number of (internal) lines in common. I wrote a program to count these numbers and the results are given in the table below. The second column gives the Catalan number for the value given in the first column. The following columns give the number of pairs that have the number of lines in common equal to the number given above the column. The total number of pairs is equal to Cn(Cn-1)/2. The diagonal sequence 1, 5, 21, 84, 330, and so on, seems to be equal to OEISsequence A002054.
n C 0 1 2 3 4 5 6 7 ----------------------------------------------------------------- 2 2 1 3 5 5 5 4 14 34 36 21 5 42 273 308 196 84 6 132 2436 2928 1992 960 330 7 429 23391 29898 21555 11220 4455 1287 8 1430 237090 321490 244420 135080 58630 20020 5005 9 4862 2505228 3594756 2872694 1670812 773773 292292 88088 19448
Trip to China 2010
-- contact -- Frans
My life as a hacker
The Art of Programming
HTML to LaTeX
eXtreme Programming Hamilton cycles