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Humanist Archives: March 27, 2020, 7:35 a.m. Humanist 33.699 - recipes and algorithms

                  Humanist Discussion Group, Vol. 33, No. 699.
            Department of Digital Humanities, King's College London
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    [1]    From: Tim Smithers 
           Subject: Re: [Humanist] 33.693: recipes and algorithms (136)

    [2]    From: Peter Van Kranenburg 
           Subject: Re: [Humanist] 33.688: recipes and algorithms: why not interactive? (33)

        Date: 2020-03-26 21:26:25+00:00
        From: Tim Smithers 
        Subject: Re: [Humanist] 33.693: recipes and algorithms

Dear Willard,

You ask, following your pseudocode and recipe examples,

   "Does the second example ... open the door to the third?"

No, certainly not, I would say.

After this message is an example of a recipe, like yours but a
bit longer, that I have rescued from a lecture I used to give
on computation and algorithms (as part of a Masters' level
course on Knowledge Representation and Inference, back in the
late 1980s).  I used this example to show how recipes clearly
differ from algorithms.  They may belong in the Zoo of ways of
doing things, but they are very different animals in that Zoo.

No CPU (able to run binary coded algorithms composed of well
defined operations on bytes of bits) that I've ever come
across would understand instructions like "to serve 6," "very
small onion," "lightly but firmly," "decorate," or "for
half-an-hour or a little longer," just to pick a few examples
of the many differences.

Suggesting that algorithms are somehow like recipes is, I
think, horribly misleading.

I take your question to be rhetorical and your message to say
the same as the above, and thank you for doing so.  It needs
saying, I think.  I follow Donald Knuth in his insisting that
computer programes should be written to be read by people,
which makes computer programs a kind of literature, but,
contrary to Knuth, this does not make the algorithms these
programs implement things like recipes, which are also a kind
of literature.

What we might want to say -- and this is what I like to think
Knuth really means to say -- is that computer programs are
like recipes.  But computer programs are not the same as the
algorithms they implement.  In a good program there is a lot
else besides the instructions needed for a CPU to correctly
execute the algorithm.  As has already been remarked, and
illustrate by you, there are instructions to do with
interaction with things like thermometers and people.  But,
just as importantly, I think, there is all the code Comments
and documentation needed to make the program readable by

Computer programs are literature like recipes, perhaps.
Algorithms are not.  They are mathematical constructions.  In
the thinking of this AI researcher and engineer.  (Which is
why, for example, I think no algorithm can be specified that,
when implemented well in a computer program, could give rise
to something that understands recipes in the way we humans do,
and which would write recipes for the same reasons.)

Best regards,


A real recipe from Betty Falk, 1964, 1973: The Beginner's
Cookery Book, Penguin Books

Recipe: Egg and Bacon Pie (page 48)

  Ingredients (to serve 6)

    6 oz streaky bacon
    4 eggs
    2 or 3 firm tomatoes
    1 very small onion
    White of egg (or milk) for glazing

    For Pastry

    14 oz plain flower
     2 oz ground rice (or semolina)
     2 teaspoons baking powder
     4 oz margarine
     4 oz lard
    Pinch salt
    About 2 tablespoons cold water


    Deep flan tin
    Large basin
    Sieve or strainer
    Rolling pin
    Chopping knife and board
    Clean cloth

  Time required: About 1.5 hours


    1 Set oven to Fairly Hot, Mark 6, 400 deg F
    2 Make pastry. Sieve all dry ingredients into basin
    3 Rub in fats with fingertips until mixture resembles
      fine breadcrumbs
    4 Add 2 tablespoons cold water gradually, mixing with
      knife, until all flour is taken up.  Form into ball
      of soft dough with fingertips
    5 Roll out lightly on lightly floured surface to about
      one quarter inch thick. Stand tin on pastry and draw a
      line round outer edge with knife. Remove dish and cut
      pastry to line it, pressing pastry lightly but firmly
      down. Re-roll and cut slightly larger circle to form
    6 Cut rinds and RUST from bacon and cut rashers into
      about three pieces.
    7 Peel and chop onion finely. Wash, dry, and slice
    8 Line bottom of pie with bacon. Then add tomatoes
      and bacon, sprinkled with onion, in layers.
    9 Break eggs over rest of ingredients, keeping them
      evenly spaced as fas as possible. It is of no
      importance if the yokes break. Sprinkle with salt
      and pepper.
   10 Lay pastry-cover on top, and knock up edges with back
      of knife, or Flute them. Cut leaves of pastry
      (elongated diamond shapes) from the trimmings and
      decorate the centre of the pie with them. Make a
      small hole in the centre with the point of a knife.
   11 Brush pie with white of egg to glaze it.
   12 Bake for half-an-hour or a little longer, until
      golden brown and risen. The eggs should be set inside.

  Serve hot or cold, decorated with sprigs of parsley.

        Date: 2020-03-26 10:17:26+00:00
        From: Peter Van Kranenburg 
        Subject: Re: [Humanist] 33.688: recipes and algorithms: why not interactive?

How can an algorithm be a "self-contained automatic machine"?

 From a technical point of view (in the context of a Von-Neumann

An algorithm is a (abstract) series of instructions. It does nothing. It
does not 'compute'. It does not 'interact'. It is not possible to 'keep'
an algorithm from doing something. It is the machine (CPU with Memory)
that 'does' something, namely executing the sequence of instructions.
More precisely: a machine (CPU and Memory) executes an implementation of
the algorithm suited for that particular machine. A user (a human or
another process on the same machine) needs to start the execution of the
algorithm (by loading the instructions in instruction memory and loading
the input data at the appropriate place in data memory and pointing the
machine to the first instruction of the algorithm). Strictly, the data
(input, memory, output) is not part of the algorithm. The data (memory
and output) changes by running the algorithm, but the algorithm itself
does not change by running it.

How to define 'interaction' in this context?

In the analogy with the cookbook recipe, the cook has the role of the
'machine'. There, the analogy is problematic, because a human does not
need exact and unambiguous instructions. A human does not have a finite
instruction set. A human is not a Von Neumann machine with instructions
and data memory strictly separated. A human is able to divert from the
cookbook instructions. A machine (CPU) is not able to divert from the
sequence of instructions that makes up the algorithm (or actually, its


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