RE : crazy run-time fluctuations (mostly super-slow) -- a bit more data

Oliver Kullmann <O.Kullmann at swansea.ac.uk> writes:
> However, with each invocation of :lisp seems to start a fresh
> environment, unrelated to the invocation before, so that between two
> Maxima-calls apparently no relation can be established between the
> calls of random??:
>
> (%i447) :lisp (setq ss *random-state*)
> #<random-state 000000000143b000>
> (%i447) :lisp (setq ss2 *random-state*)
> #<random-state 000000000143b000>
> (%i447) :lisp (equal ss ss2)
> T
> (%i447) :lisp (random 1000 ss)
> 808
> (%i447) :lisp (random 1000 ss2)
> 57
> (%i447) :lisp (equal ss ss2)
> T

If you're happy with C-like languages, the best thing is to think that
ss and ss2 are like pointers to a (complicated) structure, which is also
pointed to by *random-state*.

Thus your two calls to random are exactly the same as if you'd called
(random 1000 ss) twice.

In common lisp, equality is a funny thing. You probably meant to use
EQUAL-P here rather than EQUAL, but in fact you'll definitely get T
every time because ss and ss2 are just pointing to the same structure.

See this transcript for a way to do what I think you want:

Maxima 5.25post http://maxima.sourceforge.net
using Lisp SBCL 1.0.52.0.debian
Distributed under the GNU Public License. See the file COPYING.
Dedicated to the memory of William Schelter.
The function bug_report() provides bug reporting information.
(%i1) :lisp (defvar *ss1* (make-random-state t))

*SS1*
(%i1) :lisp (defvar *ss2* (make-random-state t))

*SS2*
(%i1) :lisp (setf *random-state* *ss1*)
*** output flushed ***

(I'm throwing away the output because it's big)

(%i1) :lisp (defvar *frozen-ss1* (make-random-state nil))

*FROZEN-SS1*
(%i1) :lisp (eq *ss1* *frozen-ss1*)

NIL
(%i1) :lisp (equalp *ss1* *frozen-ss1*)

T

(This shows that the contents of *ss1* and *frozen-ss1* are the same (as
you'd expect since *frozen-ss1* is supposed to be a copy of *ss1*). But
eq returns NIL, since they aren't in the same place in memory. As a
result when we run the next lines, *ss1* changes but *frozen-ss1* doesn't).

(%i1) :lisp (random 10)

3
(%i1) :lisp (random 10)

6
(%i1) :lisp (random 10)

5
(%i1) :lisp (random 10)

7
(%i1) :lisp (setf *random-state* *frozen-ss1*)
*** output flushed ***
(%i1) :lisp (random 10)

3
(%i1) :lisp (random 10)

6
(%i1) :lisp (random 10)

5
(%i1) :lisp (random 10)

7
(%i1) 

(Finally, let's check that *ss2* is just completely different.)

(%i1) :lisp (setf *random-state* *ss2*)
*** output flushed ***
(%i1) :lisp (random 10)

8
(%i1) :lisp (random 10)

9
(%i1) :lisp (random 10)

5
(%i1) :lisp (random 10)

8



Tada! I hope this clears things up for you to some extent.

Rupert
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