On Fri, Jan 17, 2014 at 2:24 PM, Petite Abeille <petite.abei...@gmail.com>wrote:
>
> On Jan 17, 2014, at 7:47 PM, big stone <stonebi...@gmail.com> wrote:
>
> > - I just did my first recursive CTE under Ipython notebook.
>
> Finally! We can solve sudoku puzzles in SQL :P
>
Dan Kennedy, who created the common-table-expression that just found its
way onto trunk, suggests the following query for computing the Mandelbrot
Set as ascii-art:
WITH RECURSIVE
xaxis(x) AS ( VALUES(1) UNION ALL SELECT x+1 FROM xaxis WHERE x<110),
yaxis(y) AS ( VALUES(1) UNION ALL SELECT y+1 FROM yaxis WHERE y< 30),
m(iter, xpix, ypix, x, y) AS (
SELECT 0, x, y, 0.0, 0.0 FROM xaxis, yaxis
UNION ALL
SELECT iter+1, xpix, ypix,
x*x-y*y + ((xpix * 3.5 / (SELECT count(*) FROM xaxis) - 2.5)),
2.0*x*y + ((ypix * 2.0 / (SELECT count(*) FROM yaxis) - 1.0))
FROM m
WHERE (x*x + y*y) < 4.0 AND iter<50
),
m2(iter, xpix, ypix) AS (
SELECT max(iter), xpix, ypix FROM m GROUP BY xpix, ypix
),
a(t) AS (
SELECT group_concat( substr(' .+*#', 1+min(iter/7,4), 1), '' )
FROM m2 GROUP BY ypix
)
SELECT substr(rtrim(t),15) FROM a;
Copy/paste the above query into a file called "mandelbrot.txt" then run:
./sqlite3 <mandelbrot.txt
--
D. Richard Hipp
d...@sqlite.org
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