From help-octave-request at bevo dot che dot wisc dot edu  Wed Dec 20 09:14:18 2000
Subject: Re: anonymous functions?
From: Etienne Grossmann <etienne at anonimo dot isr dot ist dot utl dot pt>
To: hanwen at cs dot uu dot nl, help-octave@bevo.che.wisc.edu
CC: etienne at isr dot ist dot utl dot pt
Date: Wed, 20 Dec 2000 15:20:00 +0000


  Hello,

From: Han-Wen Nienhuys <hanwen at cs dot uu dot nl>
#  Please bear with me, I'm a newbie user. I want to build a simple
#  meshless PDE solver in octave, but right at the start I get stuck.
#  I'm trying to write a function to compute a gram-matrix, but I can't
#  figure out how to pass an anonymous function to the quad procedure.

#  What I am hoping|trying to do:


#          function G =  grammatrix (funcs)
#            l = length (funcs)
#            G = zeros (l,l)
#            i = 0
#            j = 0
#            for f = funcs
#              for g =  funcs
#                function p = prod(t)
#                  p = f(t) * g(t)
#                endfunction
#                G(i,j) = quad (prod,0, 1, [0, 0.01], [])
#                j++
#                endfor
#              i++
#            endfor
#          endfunction

  for f = funcs
     ....
  end

  loops over the columns of funcs :

octave:52> for ii = reshape (1:6,2,3), ii, end
ii =

  1
  2

ii =

  3
  4

ii =

  5
  6

  which may not be what you expected.

  You may do 

  eval (["function p = my_prod(t)\n"\
          "  p = f(t) * g(t);\n"\
          "endfunction\n"]);

  but f(t) will not be visible (see the man pages on local and global
variables); by default, all vars are local.

  Also, you don't get an anonymous func : it's called "my_prod". (note
that "prod" is a builtin function). Do you usually program in perl (a
good language for anonymous functions)?

  Sorry for not being very helpful,

  Etienne









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