[PYTHON MATRIX-SIG] 2 Bugs? and: Mandelbrot: another nice useless NumPy script?!

[Rob.Hooft@embl-heidelberg.de]

I guess a lot of you have seen the nice posting on c.l.python where
Guido explains the fact that "lambda" can be used to obfuscate python
code beyond belief.  I decided to rewrite the mandelbrot script he
sent there. First I did it in plain python (will post to c.l.python
later). My unobfuscated version was about 2 times faster than the
original :-)

But: if one wants to make a really fast python script with vector
code: why not use Numeric python. The result (3 times faster than the
fastest plain python version I could get) is appended to this mail.

To make this message at least a bit useful: are the following two
problems (which I ran in to while coding this) effect of a known bug
in NumPy1.0a2?

  Python 1.4b3 (Aug 31 1996)  [GCC 2.7.2p snapshot 960816]
  Copyright 1991-1996 Stichting Mathematisch Centrum, Amsterdam
  >>> from Numeric import *
  >>> z=array(6*[0j])
  >>> z**2                      # v         v   Why are these not zero?
   (0.+0.j)  (0.+0.j)  (0.+0.j)  (1.+0.j)  (1.+0.j)  (0.+0.j)
  >>> `z`
  "array([0j, 0j, 0j, 0j, 0j, 0j], 'D')"
  >>> z=array(6*[0j],Complex)
  >>> z
   0.  0.  0.  0.  0.  0.   ### <==== Hey, these are reals!!!!
  >>> `z`
  "array([0.0, 0.0, 0.0, 0.0, 0.0, 0.0], 'd')"

Regards,

Rob Hooft.
--------------------------------------------------------
#!/bin/env python
#
# Mandelbrot ASCII-art using Numeric Python 1.0alpha2
#
# Rob Hooft, 1996. Distribute freely.

from Numeric import *

def draw(LowX, HighX, LowY, HighY, stepx=80, stepy=24, maxiter=30):
    xx=arange(LowX,HighX,(HighX-LowX)/stepx)
    yy=arange(HighY,LowY,(LowY-HighY)/stepy)*1j
    c=ravel(xx+yy[:,NewAxis])
    z=zeros(c.shape,Complex)
    output=resize(array(['_'],'c'),c.shape)
    for iter in range(maxiter):
	z=z*z+c
	finished=greater(abs(z),2.0)
	c=where(finished,0+0j,c)
	z=where(finished,0+0j,z)
	output=where(finished,chr(66+iter),output)
    return add.reduce(output)


if __name__ == "__main__":
    print draw(-2.1, 0.7, -1.2, 1.2)


-- 
=== Rob.Hooft@EMBL-Heidelberg.DE   http://www.Sander.EMBL-Heidelberg.DE/rob/ ==
==== In need of protein modeling?  http://www.Sander.EMBL-Heidelberg.DE/whatif/
Validation of protein structures?  http://biotech.EMBL-Heidelberg.DE:8400/ ====
== PGPid 0xFA19277D == Use Linux!  Free Software Rules The World! =============

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