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33 321 3111 222 221I 2IIII IIIIII

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Originally appearing in Volume V19, Page 866 of the 1911 Encyclopedia Britannica.
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33 321 3111 222 221I 2IIII See also:

IIIIII  , where no See also:part is greater than 3; and so in See also:general we have the theorem, the number of partitions of n into not more than k parts is equal to the number of partitions of n with no part greater than k . We have for the number of partitions an See also:analytical theory depending on generating functions; thus for the partitions of a number n with the parts 1, 2, 3, 4, 5, &c., without repetitions, See also:writing down the product I +x. r +x2 . I +x3 . I +x4 ... , = I +x+x2 -2X3 ... +Nx^+ ... , it is clear that, if xa, x13, xY, . are terms of the See also:series x, x2, x3, for which a+3+—y+ =n, then we have in the development of the product a See also:term x", and hence that in the term Nx" of the product the coefficient N is equal to the number of partitions of n with the parts 1, 2, 3, ... , without repetitions; or say that the product is the generating See also:function (G . F.) for the number of such partitions . And so in other cases we obtain a generating function . Thus for the function 1 I — x I—x2 . -x3 .

. . =+x+2x2+.,+Nx"+,,,, observing that any See also:

factor 1/r —x1 is=l+x1+x21+ ... , we see that in the term Nx" the coefficient is equal to the number of partitions of n, with the parts 1, 2, 3, . . , with repetitions . Introducing another See also:letter z, and considering the function I+xz.I+x2z.I+x3z . . .,=l+z(x+x2+ . .)...+Nx"zk+, we see that in the term Nx"zk of the development the coefficient N is equal to the number of partitions of n into k parts, with the parts 1, 2, 3, 4, , without repetitions . And similarly, considering the function - xZ . I - I x3Z . .' =I+z(x+x2+..)...+Nx"zk+ .. Ix22.- we see that in the term Nx"zk of the development the coefficient N is equal to the number of partitions of n into k parts, with the parts I, 2, 3, 4, , with repetitions . We have such analytical formulae as I-xZ.I-x22.I-x3Z .

I +I — , x+ r—x I-x2+" which See also:

lead to theorems in the See also:partition of See also:numbers . A remarkable theorem is I -x . I -x2 . I -x3 . I -x4 . = I -x-x2+x5+x7-x12-x15+ ... , where the only terms are those with an exponent z (3n2 tn), and for each such pair of terms the coefficient is The See also:formula shows that except for numbers of the See also:form 2(3n2tn) the number of partitions without repetitions into an See also:odd number of parts is equal to the number of partitions without repetitions into an even number of parts, whereas for the excepted numbers these numbers differ by unity . Thus for the number II, which is not an excepted number, the two sets of partitions are II, 821, 731, 641, 632, 542 10.1,92, 83, 74, 65, 5321, in each set 6 . We have r—x.1+x.I+x2.I+x4.1+x2 ... =1; or, as this may be written, 1+x . I +x2 . I +x4 .

I +x8 ... = I I x, = I +x+x2-{-x3+ ... , showing that a number n can always be made up, and in one way only, with the parts 1, 2, 4, 8, . The product on the See also:

left-See also:hand See also:side may be taken to k terms only, thus if k=4, we have 18 I +x.I +x2 . I +x4.I +.',C8,= _ 1I x '=i+x+x2...+x15, number or of the successive numbers 1, 2, 3, &c . And of course in any See also:case, having obtained the partitions, we can See also:count them and so obtain the number of partitions . Another method is by L . F . A . See also:Arbogast's See also:rule of the last and the last but one; in fact, taking the value of a to be unity, and, understanding this letter in each term, the rule gives b; c, b1 d, bc, b3; e, bd, c2, b2c, b4, &c., which, if b, c, d, e, &c., denote I, 2, 3, 4, &c., respectively, are the partitions of 1, 2, 3, 4, &c., respectively . An important notion is that of conjugate partitions . zx 22x2 11 that is, any number from t to 15 eau be made up, and in one way only, with the parts 1, 2, 4, 8; and similarly any number from 1 to 2k—I can be made up, and in one way only, with the parts 1, 2, 4, ..

2k-1 . A like formula is I—x3 1—x9 1—x27 1—x31 1—x81 x.I— x x3.I—x3 x9 . I—x9 x27.I—x27 x40.I—x' that is, x'+I+x.x 3+I+x3.x-9+I+x9.x'7+I+x27 =x-40+x-39 . +I+x ... +x39+x90, showing that any number from -40 to +40 can be made up, and that in one way only, with the parts 1, 3, 9, 27 taken positively or negatively; and so in general any number from -s(3k-I) to +(3k-1) can be made up. and that in one way only, with the parts t, 9, . . 3k-' taken positively or negatively . See further COMBINATORIAL See also:

ANALYSIS . (A .

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