# A Discipline of Programming by Edsger W. Dijkstra By Edsger W. Dijkstra

He starts off via contemplating the questions, «What is an algorithm?» and «What are we doing after we program?» those questions lead him to an attractive digression at the semantics of programming languages, which, in flip, results in essays on programming language constructs, scoping of variables, and array references. Dijkstra then offers, as promised, a set of lovely algorithms. those algorithms are a ways ranging, overlaying mathematical computations, several types of sorting difficulties, trend matching, convex hulls, and extra. simply because this can be an previous e-book, the algorithms provided are often not the easiest on hand. even though, the worth in analyzing A self-discipline of Programming is to take in and comprehend the best way that Dijkstra thought of those difficulties, which, in many ways, is extra priceless than one thousand algorithms.

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Y , . anya’1 112. Y? 8) a1 + a t + + a,, = n - 1. 9) Indeed, this is true for X , and A’,. 10) and therefore also becomes of the dimension n. 8) a1 + 2u2 + 3a3 + ... + nu,, = 2n - 2. 1 1) This is true for XI and X,. 1 1) true for an n. 10) obviously raises the total weight of each term of X,, also by 2. 7. 12) while the lowest term in X,, and the only term not containing any yv with v>2is ( - 1)” - 1 1 . 3 . (2n - 3) y;- 1 (n 2 2). 13) Indeed, our assertions are obviously true for X,. Suppose that they are true for an n.

5. ,n + l ) . ,Y ( ~ )This . is true for n = 0,l. We have, in particular, X , = 1, X , = -y". Assume the truth of our assertion for the first n derivatives of cp(y). 5) with k = n and get by differentiation, since dy'ldy = y"/y', 1 ( 2 n - I ) X Y" -y'-? 5) x,+,= (Xn),'yt - ( 2 n - l ) X , y". 7) 6. In Sections 6-8 (and in Appendix C ) we write y, instead of y('). ,y , . anya’1 112. Y? 8) a1 + a t + + a,, = n - 1. 9) Indeed, this is true for X , and A’,. 10) and therefore also becomes of the dimension n.

Proof. By Darboux’s theorem,f’(x) has a constant sign throughout J,, and thereforef(x) is strictly monotonic in J, and cannot have there more than one root. Without loss of generality, assumef(x,) > 0. Let Minf(x) =f (0 (x E Jx , r E JJ. We have two cases to consider: Case 1. If f ( 5 ) < 0, then the theorem is proved, for if f(<) = 0, the assertion is evident; and iff(<) 0, sincef(x,) > 0, there is a point between and xo at whichf(x) = 0. -= < Case II. f(l)> 0. By the mean value theorem of differential calculus, f (xo) -f(t)= (xo - t;) f ’ ( P ) , f(X0) > f(x0) - f ( O = 1x0- 51 IS’(P>l, f(x0) > Ixo-tlm.