macrakis at alum.mit.edu
Tue May 22 11:57:28 CDT 2007
On 5/21/07, Thomas Widlar <twidlar at yahoo.com> wrote:
> The original file is about 3.12MB, about 208,000 floating point numbers
> of zero. I tried it again. About an hour later, wxmaxima still says
is calculating" consuming 99% of the CPU.
I took a look at the code. It is clearly not intended for large inputs, as
read_list contains an n^2 algorithm, where it repeatedly appends to the
*end* of an accumulation list, requiring n^2/2 cons's. At the cost of
slightly trickier code, we can improve efficiency for large inputs. Here's
the performance comparison on GCL, 1GHz, W2k:
Size Count Old time New time
75k 15,000 3 sec 2 sec
150k 30,000 14 sec 5 sec
300k 60,000 64 sec 11 sec
I didn't have the patience to try larger files...
I'm updating the code in CVS, and including it below.
(defun $read_list (file-name &optional sep-ch-flag)
(let ((A '()) (L))
(setq file-name (require-string file-name))
(with-open-file (in file-name :if-does-not-exist nil)
((not (null in))
(let ((sep-ch (get-input-sep-ch sep-ch-flag file-name)))
(setq L (read-line in nil 'eof))
(if (eq L 'eof)
(return (cons '(mlist simp) (nreverse A))))
(setq A (nreconc (cdr (make-mlist-from-string L sep-ch)) A)))))
(t (merror "read_list: ~S: no such file" file-name))))))
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