{"id":235,"date":"2016-06-15T11:37:27","date_gmt":"2016-06-15T09:37:27","guid":{"rendered":"http:\/\/www.hunggartorino.it\/ql\/?p=235"},"modified":"2016-05-13T14:55:32","modified_gmt":"2016-05-13T12:55:32","slug":"numeri-casuali-e-ql","status":"publish","type":"post","link":"https:\/\/www.hunggartorino.it\/ql\/numeri-casuali-e-ql\/","title":{"rendered":"QL and random numbers"},"content":{"rendered":"

Recently in the Italian mailing list we’ve discussed about the real randomness of the “random” numbers created by QL through its command RND.<\/p>\n

Unlike<\/span> on the<\/span> ZX<\/span> Spectrum<\/span>, whose corresponding<\/span> function<\/span> will never generate<\/span> certain values<\/span>, on QL<\/span> the numbers seem<\/span> really<\/span> random<\/span>.<\/span><\/p>\n

Let’s try with a simple three lines program:<\/p>\n

REPeat CR_POINTS
\nPOINT RND(255),RND(255)
\nEND REPeat<\/p><\/blockquote>\n

This program is supposed to print random points, therefore the displayed rectangle should be completely filled after some time.<\/p>\n

\"Immagine\"<\/a><\/p>\n

From<\/span> first glance<\/span> it appears that<\/span> some areas<\/span> are<\/span> titally improbable<\/span> because<\/span> there are<\/span> “holes<\/span>” and rows<\/span> where<\/span> QL<\/span> will never<\/span> print points<\/span>. In<\/span> fact, the<\/span> proposed program<\/span> is not complete<\/span> because<\/span> there is not only<\/span> POINT<\/span>, but also other<\/span> commands and<\/span> methods to draw<\/span> points<\/span> on the<\/span> QL<\/span>: PLOT<\/span> (<\/span>to be loaded<\/span>, non-native<\/span> in Qdos<\/span>) and<\/span> BLOCK<\/span>. A<\/span> mailing list<\/span> user (<\/span>“<\/span>CRX<\/span>“<\/span>) analyzed this issue<\/span> and<\/span> made some tests<\/span> with the three<\/span> keywords adding color<\/span>. We get<\/span> different results<\/span>.<\/span><\/p>\n

100 REMark *** RANDOMNESS ***\r\n110 REMark ~~~~~~~~~~~~~~~~~~\r\n120 MODE 8: PAPER 0\r\n130 WINDOW 512,256,0,0: CLS\r\n140 INK 5: CSIZE 0,1: CURSOR 77,130: PRINT \"Point       Block      Plot\"\r\n150 :\r\n160 FOR points=1 TO 3000\r\n170   POINT RND(22 TO 40),RND(60 TO 80)\r\n180   INK RND(1 TO 7)\r\n190 END FOR points\r\n200 :\r\n210 FOR blocks=1 TO 5000\r\n220   BLOCK 2,1,RND(218 TO 280),RND(50 TO 100),RND(1 TO 7)\r\n230 END FOR blocks\r\n240 :\r\n250 REMark ** Requires PLOT & DRAW **\r\n260 REMark ~~~~~~~~~~~~~~~~~~~~~~~~~~\r\n270 :\r\n280 FOR plots=1 TO 5000\r\n290   PLOT RND(350 TO 410),RND(50 TO 100)\r\n300   INK RND(1 TO 7)\r\n310 END FOR plots<\/pre>\n
\"4casi\"<\/a><\/p>\n
In all<\/span> cases<\/span> POINT<\/span> never<\/span> fills<\/span> the rectangle<\/span> but<\/span> puts<\/span> the pixels<\/span> following<\/span> a sort of grid<\/span>, both<\/span> on<\/span> real<\/span> QL<\/span> and<\/span> on<\/span> emulator<\/span>. With\u00a0<\/span> recent<\/span> Minerva<\/span> ROM, colors appear<\/span> anything but random<\/span>. With<\/span> older Minerva<\/span> and<\/span> JS<\/span> ROMs\u00a0 instead,<\/span> everything seems<\/span> more random<\/span>…<\/span> but<\/span> observing carefully<\/span> we realize<\/span> that the pixels<\/span> are arranged<\/span> in exactly the<\/span> same scheme<\/span> and with the same<\/span> colors.<\/span> Since the<\/span> internal clock<\/span> of basic QL<\/span> has no<\/span> backup battery,<\/span> it<\/span> resets<\/span> every time you turn on the computer<\/span>; therefore<\/span> the <\/span>he RND function<\/span>, which<\/span> is given by<\/span> a count<\/span> in fractions<\/span> of a second<\/span> starting from<\/span> the<\/span> QL<\/span> power on<\/span>,<\/span> can be<\/span> modified<\/span> with the<\/span> RANDOMISE<\/span> statement<\/span>.<\/span><\/p>\n
For example, with the command:
\nRANDOMISE DATE
\nwe get immediatly more random-looking rectangles, avoiding the “rainbow effect”.<\/p>\n
As for<\/span> the holes that<\/span> visible<\/span> with<\/span> POINT<\/span> compared<\/span> to other<\/span> commands<\/span>,<\/span> actually<\/span> it is due<\/span> to the fact that<\/span> POINT<\/span>, unlike<\/span> BLOCK<\/span> and<\/span> PLOT<\/span>, uses the<\/span> graphic coordinate system and<\/span> not<\/span> the pixels.<\/span> Therefore<\/span> it requires<\/span> coordinates with<\/span> fractional<\/span> values<\/span> also (<\/span>POINT<\/span> 3.5,8.5<\/span>) in order to<\/span> switch on all the<\/span> pixels<\/span>, while RND<\/span> provides only<\/span> integers<\/span>.<\/span><\/span><\/p>\n
 <\/p>\n
Photo: red numbers <\/a>\u00a0 by DaveBleasdale \/\u00a0 CC BY\u00a0 <\/span><\/a><\/em>\/ Blurred from original<\/em><\/span><\/p>\n","protected":false},"excerpt":{"rendered":"Recently in the Italian mailing list we’ve discussed about the real randomness of the “random” numbers created by QL through its command RND. \n [..more...]<\/a>","protected":false},"author":3,"featured_media":318,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[51],"class_list":["post-235","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-senza-categoria","tag-programmazione-en"],"_links":{"self":[{"href":"https:\/\/www.hunggartorino.it\/ql\/wp-json\/wp\/v2\/posts\/235","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.hunggartorino.it\/ql\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.hunggartorino.it\/ql\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.hunggartorino.it\/ql\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/www.hunggartorino.it\/ql\/wp-json\/wp\/v2\/comments?post=235"}],"version-history":[{"count":8,"href":"https:\/\/www.hunggartorino.it\/ql\/wp-json\/wp\/v2\/posts\/235\/revisions"}],"predecessor-version":[{"id":370,"href":"https:\/\/www.hunggartorino.it\/ql\/wp-json\/wp\/v2\/posts\/235\/revisions\/370"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.hunggartorino.it\/ql\/wp-json\/wp\/v2\/media\/318"}],"wp:attachment":[{"href":"https:\/\/www.hunggartorino.it\/ql\/wp-json\/wp\/v2\/media?parent=235"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.hunggartorino.it\/ql\/wp-json\/wp\/v2\/categories?post=235"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.hunggartorino.it\/ql\/wp-json\/wp\/v2\/tags?post=235"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}