code for the transpose of a list of lists.

Using Clozure Common Lisp, your array based transpose seems to be fast:

 (%i6) m : genmatrix(lambda([i,j],i), 600,600)$

 (%i8) transpose(m)$
 Evaluation took 0.1100 seconds (0.1090 elapsed)

 (%i9) mtrans(m)$
 Evaluation took 0.0780 seconds (0.0780 elapsed)

But as you observed, the array based transpose is slow under GCL:

 (%i12) transpose(m)$
  Evaluation took 0.3900 seconds (0.3900 elapsed)

 (%i13) mtrans(m)$
  Evaluation took 1.4700 seconds (1.4700 elapsed)

By the way: Matrix multiplication requires a transpose for a list of lists. I tried a few
experiments at speeding up matrix multiplication, but didn't get anywhere. Maybe somebody
else would like to try. An array method might be fast for non-GCL Maxima. Also, adding the
members of an inner product en masse might some be faster for some non-numeric matrices.

--Barton

-----maxima-bounces at math.utexas.edu wrote: -----

>To:?Barton?Willis?<willisb at unk.edu>,?Maxima?List?<maxima at math.utexas.edu>
>From:?Richard?Fateman?<fateman at cs.berkeley.edu>
>Sent?by:?maxima-bounces at math.utexas.edu
>Date:?06/28/2010?11:37PM
>Subject:?Re:?[Maxima]?code?for?the?transpose?of?a?list?of?lists.
>
>?Here's?another?program?to?time...
>
>(defun?$mtrans(r)?;;?r?must?be?a?maxima?matrix
>?????
>??(let*?((j?(1-?(length?r)))
>?????(k?(1-?(length?(cadr?r))))
>?????(M?(make-array?(list??j?k)?:initial-contents
>????????????(mapcar?#'cdr?(cdr?r)))))
>????(cons?'($matrix?simp)
>??????(loop?for?ind2?fixnum?from?0?below?k?collect
>??????(cons?'(mlist?simp)
>????????(loop?for?ind1?fixnum?from?0?below?j?collect
>????????(aref?M?ind1?ind2)))))))
>
>It?appears?to?be?slow?on?GCL,?but?may?be?much?faster?on?some?other?lisps.
>
>I?also?don't?know?about?optimization?settings?for?GCL?etc.
>
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