Hi there,

Really xlisp-stat is closer and closer to common lisp, and that's good news. 
Look at this:

In the Common Lisp The Language book (now electronically available!)
there is a set of lisp function to draw graphs of complexs functions.
One of them is in the book cover, the other are in pages 317ff. 

I took the lisp sources and with a few modifications it run in
xlisp-stat. I think  that it's interesting by itself and also as a
good example of how to generate postscript coded graphs form xlisp.

The main function is 
picture &optional (function 'sqrt)

For example, (picture 'identity) will dump to a file named identity.ps
a postscript description of the identity function graph, that is
actually the mesh that is used in this kind of complex graphs.


PROBLEMS:

I think there is an error in the declaration of the function picture,
as it must be 
picture &optional (function 'sqrt)
and not 
picture &optional (function #'sqrt)
but I don't know if correcting CLTL is a sacrilege.

Strangely, there are a few lines missing at random in the electronic
version of the listing. I added them manually from the hardpaper
version of the book.


xlisp-stat does not conform to CL in function signum.
According CL, signum over a complex must give a complex with the same
phase and unit length. My quick-hack for it has been:
(defun my-signum (num)
  (if (complexp num)
      (if (= #C(0 0) num)
	  num
	(/ num 
	   (sqrt (* num (conjugate num)))))
    (signum num)))


some CL global constants are not defined, I took the values that gcl
has:

(defparameter most-positive-single-float 1.797693134862316E308)
(defparameter least-positive-single-float 4.9406564584124654E-324)

I have modified also the postscript header and added a 'showpage' at
the end of the generated file.

Enjoy it, try (picture 'cos), it's nice.



-- 

Frederic Udina
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