From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me X-Spam-Level: X-Spam-Status: No, score=0.1 required=5.0 tests=BAYES_05,INVALID_MSGID autolearn=no autolearn_force=no version=3.4.4 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: 103376,a0ad312f61fa680d,start X-Google-Attributes: gid103376,public From: G M Wallace Subject: vectors, spacetime Date: 1999/11/19 Message-ID: <3834BEAB.13F5B232@interact.net.au>#1/1 X-Deja-AN: 550382966 Content-Transfer-Encoding: 7bit Organization: Humanity X-Accept-Language: en Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 Newsgroups: comp.lang.ada Date: 1999-11-19T00:00:00+00:00 List-Id: Ok. I will keep trying to ask for information coz I am doing the self-education thing. I realise this place is inhabited by professional programmers and I am grateful for any and all help given to me and my remedial questions. Remember - this is also part of a philosophical study for me. 2 questions 2day. 1) I have been looking through a physics textbook and thinking about Ada. I have certainly come across VECTORS in the source code for a variety of things. I am wondering this - if a vector has (or can have) several parameters - and in defining something like the wind flow patterns over land or sea (as in weather images with the zillions of little arrows pointing with wind flow direction) - would it be right to define a vector as a record with several properties (speed, direction, accelleration, etc.) and then construct a multidimensional array of such records ? Or is a vector only applicable to single qualities - like speed, direction, etc. There is probably some much simpler solution. Yes, this may be a more general question but in asking ada programmers I see the way you think about such things. OK. 2) (The answers I may or may not get on this question will undoubtedly be a little bit beyond me but I would appreciate and and all contributions from amateurs or professionals who frequent comp.lang.ada). If someone was to attempt to computationally represent a spacetime system in terms of three dimensions of space and one dimension of time, because time is a 'negative' quality in relativistic equations, does that create insurmountable probelsm of definition and reference ? The square root of -1 is a complex number and i am aware that there ARE ada packages to deal with such things. However - in spacetime it is possible to rotate the four dimensional axes relative to an initial point of reference in much the same way one may rotate a three dimensional frame in everyday (i.e. intuitive) space. In the case where one must account for two different inertial frames of reference - the four dimensional 'wire-frame' metric may indeed be rotated. In this case - and quite literally with experimental verification, spatial and temporal dimensions may rotate into one another - what is distance for one observer may become duration for another - and all the possible anamorphic distortions between such ideal cases. (Granted that we have to be talkling about significant velocities or gravitational masses before the effects become anything like dramatic). Are the three space and one temporal dimensions thus to be cast as all of the same type ? What, then, of the fact that the thre espatial dimensions are rendered as positive numbers and the temporal as a negative. (I am aware of the fact that there can be problems with types when certain measurement units are employed). Would one cast something like : ------------------------------- -- spacetime.ads ------------------------------ package spacetime is type unit is new integer; type dimension is abstract tagged null record; type dimension_access is access dimension; type spatial_unit is new dimension with record coord : unit; end record; type temporal_unit is new dimension with record coord : unit; end record; end spacetime; --------------------------------- Of course, I don't know what happens at deeper levels. The whole business with the compatibility of time as negative one sqaured and as x, y, and z as positive numbers squared and then the ability to trasnfer (or partially so) quantities and measurement form one fram to another is something I understand conceptually more than computationally. And even if no one responds, it helps me heaps to work out more to put it up here coz I have to think it through in a presentable form. p.s. In terms of spacetime - there exists one inertial frame of reference such that a projectile travelling at (an idealised) constant velocity can be 'seen' from another inertial frame as existing simultaneously at every point on its journey. Makes new sense of the Zen archery (Kyudo) concept of man, bow, arrow and target all 'being one'. :-) -- Graeme Wallace Canberra Australia "He attracted some attention / When he discovered the fourth dimension / But he ain't got rhythm / So no one's with him / The loneliest man in town" -- 1940's song lyric.