Sketch of the Analytical Engine invented by Charles Babbage, Esq.Menabrea, Luigi Federico
Science
Sketch of the Analytical Engine invented by Charles Babbage, Esq.
Menabrea, Luigi Federico
Babbage, Charles, 1791-1871; Numerical analysis
Six numerical data are in this case necessary for making
the requisite combinations. These data are 1, 2, (= 4),
, , . Were = 5,
the additional datum , would be needed. Were = 6,
the datum , would be needed; and so on. Thus the
actual number of data needed will always be , for ;
and out of these data, () of them
are successive Numbers of Bernoulli. The reason why the Bernoulli
Numbers used as data, are nevertheless placed on Result-columns
in the diagram, is because they may properly be supposed to have
been previously computed in succession by the engine itself;
under which circumstances each will appear as a
result, previous to being used as a datum for computing
the succeeding . Here then is an instance (of the kind
alluded to in Note D.) of the same Variables filling more than one
office in turn. It is true that if we consider our computation of
, as a perfectly isolated calculation, we may
conclude , , , to have
been arbitrarily placed on the columns; and it would then perhaps be
more consistent to put them on , ,
as data and not results. But we are not taking
this view. On the contrary, we suppose the engine to be in the
course of computing the Numbers to an indefinite extent, from the
very beginning; and that we merely single out, by way of example,
one amongst the successive but distinct series of computations
it is thus performing. Where the ’s are fractional, it
must be understood that they are computed and appear in the notation
of decimal fractions. Indeed this is a circumstance that
should be noticed with reference to all calculations. In any of the
examples already given in the translation and in the Notes, some of
the data, or of the temporary or permanent results, might be
fractional, quite as probably as whole numbers. But the arrangements
are so made, that the nature of the processes would be the same as for
whole numbers.
In the above table and diagram we are not considering the signs of any
of the ’s, merely their numerical magnitude. The engine
would bring out the sign for each of them correctly of course, but we
cannot enter on every additional detail of this kind, as we
might wish to do. The circles for the signs are therefore intentionally
left blank in the diagram.
Operation-cards 1, 2, 3, 4, 5, 6 prepare are
Thus, Card 1 multiplies two into , and the three
Receiving Variable-cards belonging respectively to
, , , allow the result
to be placed on each of these latter columns (this being a
case in which a triple receipt of the result is needed for subsequent
purposes); we see that the upper indices of the two Variables used,
during Operation 1, remain unaltered.
We shall not go through the details of every operation singly, since
the table and diagram sufficiently indicate them; we shall merely
notice some few peculiar cases.
Public-domain text, read in full here on John Shaqi.
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