Page:Scientific Memoirs, Vol. 3 (1843).djvu/694

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684
L. F. MENABREA ON BABBAGE'S ANALYTICAL ENGINE.

following[1] very simple example, in which we are to multiply \scriptstyle{(a+bx^1)} by \scriptstyle{(A+B\cos^1 x)}. We shall begin by writing \scriptstyle{x^0}, \scriptstyle{x^1}, \scriptstyle{\cos^0 x}, \scriptstyle{\cos^1 x}, above the columns \scriptstyle{\mathbf{V}_0}, \scriptstyle{\mathbf{V}_1}, \scriptstyle{\mathbf{V}_2}, \scriptstyle{\mathbf{V}_3}; then, since from the form of the two functions to be combined, the terms which are to compose the products will be of the following nature, \scriptstyle{x^0.\cos^0 x}, \scriptstyle{x^0.\cos^1 x}, \scriptstyle{x^1.\cos^0 x}, \scriptstyle{x^1.\cos^1 x}; these will be inscribed above the columns \scriptstyle{\mathbf{V}_4}, \scriptstyle{\mathbf{V}_5}, \scriptstyle{\mathbf{V}_6}, \scriptstyle{\mathbf{V}_7}. The coefficients of \scriptstyle{x^0}, \scriptstyle{x^1}, \scriptstyle{\cos^0 x}, \scriptstyle{\cos^1 x} being given, they will, by means of the mill, be passed to the columns \scriptstyle{\mathbf{V}_0}, \scriptstyle{\mathbf{V}_1}, \scriptstyle{\mathbf{V}_2} and \scriptstyle{\mathbf{V}_3}. Such are the primitive data of the problem. It is now the business of the machine to work out its solution, that is to find the coefficients which are to be inscribed on \scriptstyle{\mathbf{V}_4}, \scriptstyle{\mathbf{V}_5}, \scriptstyle{\mathbf{V}_6}, \scriptstyle{\mathbf{V}_7}. To attain this object, the law of formation of these same coefficients being known, the machine will act through the intervention of the cards, in the manner indicated by the following table:—

[2]
Columns
above which
are written
the functions
of the
variable.
Coeffi­cients. Cards of the
operations.
Cards of the variables.
Given. To be formed. Number
of the operations.
Nature
of the operation.
Columns
on which
operations
are to be
performed.
Columns
on which
are to be
inscribed
the results
of the
operations.
Indication of
change of value
on any column
submitted to
an operation.
Results of the operation.
\scriptstyle{x^0\ldots\ldots\ldots^1\mathbf{V}_0} \scriptstyle{a} " " " " " " " "
\scriptstyle{x^1\ldots\ldots\ldots^1\mathbf{V}_1} \scriptstyle{b} " " " " " " " "
\scriptstyle{\mathrm{Cos}^0 x\ldots^1\mathbf{V}_2} A " " " " " " " "
\scriptstyle{\mathrm{Cos}^1 x\ldots^1\mathbf{V}_3} B " " " " " " " "
\scriptstyle{x^0\cos^0 x..^0\mathbf{V}_4} \scriptstyle{a}A 1 \scriptstyle{\times} \scriptstyle{^1\mathbf{V}_0\times^1\mathbf{V}_2=} \scriptstyle{^1\mathbf{V}_4\ldots\ldots} \scriptstyle{\left\{\begin{align}&\scriptstyle{^1\mathbf{V}_0=^1\mathbf{V}_0}\\&\scriptstyle{^1\mathbf{V}_2=^1\mathbf{V}_2}\end{align}\right\}} \scriptstyle{^1\mathbf{V}_4=a}A coefficients of \scriptstyle{x}
\scriptstyle{x^0\cos^1 x..^0\mathbf{V}_5} \scriptstyle{a}B 2 \scriptstyle{\times} \scriptstyle{^1\mathbf{V}_0\times^1\mathbf{V}_3=} \scriptstyle{^1\mathbf{V}_5\ldots\ldots} \scriptstyle{\left\{\begin{align}&\scriptstyle{^1\mathbf{V}_0=^0\mathbf{V}_0}\\&\scriptstyle{^1\mathbf{V}_3=^1\mathbf{V}_3}\end{align}\right\}} \scriptstyle{^1\mathbf{V}_5=a}B … … \scriptstyle{x}
\scriptstyle{x^1\cos^0 x..^0\mathbf{V}_6} \scriptstyle{b}A 3 \scriptstyle{\times} \scriptstyle{^1\mathbf{V}_1\times^1\mathbf{V}_2=} \scriptstyle{^1\mathbf{V}_6\ldots\ldots} \scriptstyle{\left\{\begin{align}&\scriptstyle{^1\mathbf{V}_1=^1\mathbf{V}_1}\\&\scriptstyle{^1\mathbf{V}_2=^0\mathbf{V}_2}\end{align}\right\}} \scriptstyle{^1\mathbf{V}_6=b}A … … \scriptstyle{x}
\scriptstyle{x^1\cos^1 x..^0\mathbf{V}_7} \scriptstyle{b}B 4 \scriptstyle{\times} \scriptstyle{^1\mathbf{V}_1\times^1\mathbf{V}_3=} \scriptstyle{^1\mathbf{V}_7\ldots\ldots} \scriptstyle{\left\{\begin{align}&\scriptstyle{^1\mathbf{V}_1=^0\mathbf{V}_1}\\&\scriptstyle{^1\mathbf{V}_3=^0\mathbf{V}_3}\end{align}\right\}} \scriptstyle{^1\mathbf{V}_7=b}B … … \scriptstyle{x}

It will now be perceived that a general application may be made of the principle developed in the preceding example, to every species of process which it may be proposed to effect on series submitted to calculation. It is sufficient that the law of formation of the coefficients be known, and that this law be inscribed on the cards of the machine, which will then of itself execute all

  1. See Note E.
  2. For an explanation of the upper left-hand indices attached to the \scriptstyle{\mathbf{V}}'s in this and in the preceding Table, we must refer the reader to Note D, amongst those appended to the memoir.—Note by Translator.