beginner: function definition confusion

[Jeff Abrahamson]

I'm confused trying to use nlfilter.  (The ultimate goal is to do
convolutions on images.)  I'm not sure if I'm misunderstanding
nlfilter or if I'm even maybe just defining the function avg
incorrectly.  Here's what I wrote

    function T1 ( )
      img = imread("black-white.png");
      blur = nlfilter(img,[3,3],avg)
    endfunction


    function ret = avg ( blk )
      ret = 0;
      for i = 1:3
        for j = 1:3
          ret += blk(i,j);
        endfor
      endfor
      ret /= 9;
    endfunction

    T1()


The error is this:
  octave:1> T1()
  error: `blk' undefined near line 22 column 14
  error: evaluating assignment expression near line 22, column 11
  error: evaluating for command near line 21, column 5
  error: evaluating for command near line 20, column 3
  [...]

Anyone see what I'm doing wrong?


Note, by contrast, that avg works in the form I thought I needed it
to:

  octave:1> m=rand(3)
  m =

    0.30486  0.74804  0.28817
    0.54096  0.62247  0.70384
    0.67811  0.58588  0.38752

  octave:2> avg(m)
  ans = 0.53998
  octave:3> 

Thanks in advance.

-- 
 Jeff

 Jeff Abrahamson  <http://www.purple.com/jeff/>    +1 215/837-2287
 GPG fingerprint: 1A1A BA95 D082 A558 A276  63C6 16BF 8C4C 0D1D AE4B



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