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tamnd's digital brain — notes, problems, research
41282 notes
We restart from the definition of the condition and first extract its actual global consequence, instead of interpreting it geometrically.
**Exercise 5.
The review identifies three genuine failures: an unjustified symmetry factor, an unsupported intermediate bound, and a mismatch between the run decomposition and the claimed inequality.
We restart from a correct decision-tree formulation and remove the unverified state model.
**Exercise 5.
Equation (39) expresses the probability that $N$ distinct keys $K_1,\dots,K_N$ hash into $N$ distinct table positions when each key is assumed to be mapped independently and uniformly into a hash tabl...
Let $I_n$ denote the internal path length of the random BST built from $n$ keys.
Start from Eq.
Let the standard heapsort “sift-down” step be denoted by the variables of Algorithm H, where a key at position $k$ is moved downward by repeatedly comparing it with its children at $2k$ and $2k+1$, an...
Let each node $P$ contain fields $\operatorname{KEY}(P)$, $\operatorname{LLINK}(P)$, $\operatorname{RLINK}(P)$, and a tag $\operatorname{RTAG}(P)\in{0,1}$.
From equation (42), $Q_o(M,N)$ is given by the finite sum Q_o(M,N)=\sum_{k=0}^{N} \binom{N}{k}\frac{k!
Let $B_h(z)$ denote the ordinary generating function in which the coefficient of $z^n$ equals the number of balanced binary trees with $n$ internal nodes and height exactly $h$.
Let $p_1, p_2, \dots, p_N$ be the probabilities that the argument equals $K_1, K_2, \dots, K_N$, with $\sum_{i=1}^N p_i = 1$.
Working
Let $T=6$ and $P=5$.
The root node compares $K_1$ and $K_2$.
Let elements arrive in a sequence at times $t = 1,2,\ldots$.
Let the table have size $M$, with $n$ stored keys and load factor $\alpha=n/M$.
Let each key $x$ in the set of 31 words have frequency $f(x)$ as given by Fig.
Let a file consist of $N$ records with totally ordered keys.
Let $(P_1,\dots,P_n)$ be uniformly distributed over the simplex $P_k>0,\quad \sum_{k=1}^n P_k = 1.$ The entropy is $H(P_1,\dots,P_n) = -\sum_{k=1}^n P_k \log P_k.$ By symmetry, $\mathbb{E}[H(P_1,\dots...
Let $p_k$ be probabilities on ${1,2,\dots,N}$ with $\sum_{k=1}^N p_k=1$.
Let $T_n$ be a binary search tree formed by inserting $n$ distinct keys in random order, each of the $n!$ permutations equally likely, using Algorithm T of Section 6.
Let $X_l$ denote the number of trie nodes on level $l$ in a random $M$-ary trie containing $N$ keys.
We restart the counting from the actual behavior of step D3, since the previous argument misidentified what is being counted.
Let $X_n$ denote the number of descents in a random permutation of ${1,2,\dots,n}$.
The reviewer’s objection is correct: simply replacing FIFO queues by LIFO stacks breaks stability.
Let the positions be $1,2,\dots,N$.
Let $T=4$, so $P=T-1=3$ and the tape-splitting polyphase merge uses the 3-way Fibonacci system defined by the third-order recurrence F_n = F_{n-1}+F_{n-2}+F_{n-3}\quad (n\ge 3), with initial values de...
Let $w_1,\dots,w_n$ be nonnegative with $w_1+\cdots+w_n=1$.
We restart from the correct structural interpretation of $S'(k)$ as an optimal **merging-based sorting cost**, and we avoid assuming any fixed decomposition into prescribed sizes.
We restart from the correct structure and avoid any use of invalid fractional-part algebra.
Let $m=1$.
**Corrected Solution to Exercise 5.
Let $S$ be the number of elevator stops required by a fixed scheduling method applied to a uniformly random permutation of the $bn$ people among the $bn$ desks.
A $t$-ary tree is a rooted ordered tree in which each internal node has at most $t$ children.
Let $T_N$ be the Coffman–Eve $M$-ary digital search tree built from $N$ independent random infinite strings over an alphabet of size $M>2$.
A 2-3 tree is a rooted ordered tree in which every internal node has either two or three children and contains respectively one or two keys, and in which all external nodes occur at the same level.
Let $T=(V,E)$ be a finite tree with positive edge lengths $\ell(e)>0$ for $e\in E$.
**9.
Stopped thinking
**Solution to Exercise 5.
Let the six admissible column types in (19) be \binom{b}{a},\quad \binom{c}{a},\quad \binom{a}{b},\quad \binom{c}{b},\quad \binom{a}{c},\quad \binom{b}{c},
Condition (b) must exclude the case $x=y$.
No.
Using the definition of intercalation, we write \beta=\text{bddad} \qquad\Longrightarrow\qquad \begin{pmatrix} a&b&d&d&d\\
If $d < c < b < a$, the canonical factorization of (12) is obtained by reversing the order of the letters in each cycle of the factorization given in (17).
False.
**Exercise 5.
Let the permutation be written in one-line form $a_1 a_2 \cdots a_9$.
**Corrected Solution for Exercise 5.
Let $p_i$ denote the position of the element $i$ in the permutation, so that $a_{p_i}=i$.
Store the permutation in an array $P$ such that $P(j)$ is the position of $j$ in the permutation.
Let the Josephus elimination process produce the sequence $x_1,x_2,\dots,x_n$, where $x_k$ is the label removed at step $k$.
Let each catalog card be considered as a record $R_j$ with a key $K_j$ that reflects the text of the card, including author, title, and date information.
Let the inversion table of a permutation $a_1a_2\cdots a_n$ be the sequence $b_1b_2\cdots b_n$, where $b_i$ is the number of entries greater than $i$ that occur to the left of $i$ in the permutation.
**Corrected Solution.
Our systems have detected unusual activity coming from your system.
The reviewer is correct.
**Exercise 4.
The statement as printed cannot be correct, since the hypothesis \[ V(z)=U(V(z)) \] makes the additional condition about the coefficients of \(U(V(z))\) vacuous.
**Exercise 4.
**Exercise 4.
Let U(z) = z + U_k z^k + U_{k+1} z^{k+1} + \cdots, \qquad k \ge 2, \quad U_k \ne 0, and
We are given a power series $U(z) = z + U_2 z^2 + U_3 z^3 + \cdots$ with power matrix $U = (u_{nk})$, where $u_n = u_{n1} = n U_n$.
Let V(z) = V_1 z + V_2 z^2 + V_3 z^3 + \cdots, \quad V_1 \neq 0, and let
Let $U(z) = U_0 + U_1 z + U_2 z^2 + \cdots, \qquad U_0 \ne 0,$ and define the _odd induced function_ $U^{(o)}(z)$ to be the power series $V(z)$ satisfying V(z) = U(z V(z)^o).
Let the power (coefficient) matrices of $U$, $V$, and $W$ be $U=(u_{jk})$, $V=(v_{nj})$, and $W=(w_{nk})$, where these matrices encode the action of the corresponding formal power series operators as...
We continue from the definitions in exercise 17.
We are asked to prove that the poweroids $V_n(x)$ satisfy xV_n(x+y) = (x+y)\sum_{k=1}^{n} \binom{n-1}{k-1} V_k(x)V_{n-k}(y), continuing from Exercise 17.
Let $U^{[n]}(z)$ denote the $n$-fold composition of $U(z)$ with itself, as in Section 4.
We are asked: > For what functions $U(z)$ does $U^{[n]}(z)$ have the simple form $z^k$ in (27)?
Let F(z)=W_0+W_1z+\cdots+W_{N-1}z^{N-1}, the truncation of $W(z)$ modulo $z^N$.
**Problem.
We are asked to compute the first $N$ coefficients of the composed power series $W(z) = U(V(z)) = U_0 + U_1 V(z) + U_2 V(z)^2 + U_3 V(z)^3 + \cdots.$ Since $V(z)$ has no constant term, $V_0 = 0$, it f...
We are asked to connect **polynomial division** with **power series division**.
We are asked to extend Algorithm L to handle the more general situation in which $W(z) = G(t) = G_1 t + G_2 t^2 + G_3 t^3 + \cdots, \qquad z = V_1 t + V_2 t^2 + V_3 t^3 + \cdots, \quad V_1 \ne 0,$ and...
We are asked to find the coefficients in the expansion x = y^{1/a} + b_2 y^{1/a + 1} + b_3 y^{1/a + 2} + \cdots, given that
For the reversion of $z = t - t^2,$ Algorithm T is applied to the general form $U_1 z + U_2 z^2 + \cdots = t + V_2 t^2 + V_3 t^3 + \cdots,$ so here $U_1 = 1,\quad U_n = 0 \ (n \ge 2), \qquad V_2 = -1,...
The solution directly constructs a bilinear algorithm that expresses all entries $c_{ij}$ of $C=AB$ as linear combinations of exactly 21 bilinear products of linear forms in the entries of $A$ and $B$...
Let $f(x) = x^{-1} - V(z).$ We seek a power series $x = W(z)$ such that $f(x)=0$, hence $W(z)^{-1} = V(z)$.
Let the original relation be $z = t + V_2 t^2 + V_3 t^3 + \cdots,$ and let its reversion be $t = z + W_2 z^2 + W_3 z^3 + \cdots.$ Reversion constructs the compositional inverse in the sense that subst...
Formula (9) expresses $W_n$ for $n \ge 1$ in terms of the coefficients $V_k$ and the previously computed $W_{n-k}$, and it contains an explicit factor $1/n$.
The solution directly constructs a bilinear algorithm that expresses all entries $c_{ij}$ of $C=AB$ as linear combinations of exactly 21 bilinear products of linear forms in the entries of $A$ and $B$...
Let $V_m$ be the first nonzero coefficient of $V(z)$; thus $V(z)=z^m\widehat V(z),\qquad \widehat V_0=V_m\ne0.$ If $U(z)=z^r\widehat U(z),\qquad \widehat U_0=U_r\ne0,$ then $\frac{U(z)}{V(z)}=z^{\,r-m...
**2.
Let $N = m_1 \cdots m_k$ and consider a polynomial chain computing the discrete Fourier transform as a linear transformation $y = Fx,$ where $F$ is the $N \times N$ Fourier matrix with entries $\omega...
Let $T=(t_{ijk})$ be an $m\times n\times s$ tensor with rational entries.
**Solution.
Let a quasipolynomial chain compute $f(x_1,\ldots,x_n).$ Write the chain values as $v_1,\ldots,v_N,$ where each $v_i$ is either an input variable, a constant, or is obtained from earlier values by one...
X=\begin{pmatrix} x&u\\ e&Y \end{pmatrix},
Let $f(x_1,\ldots,x_n)=\sum_{1\le i<j\le n} x_i x_j.$ We count arithmetic complexity in the sense of straight-line programs: each multiplication is one operation, each addition is one operation, and i...
No.
Let $T(m,n,s)$ denote the tensor associated with multiplying an $m \times n$ matrix by an $n \times s$ matrix.
**Statement.
Let $M(n) = \operatorname{rank}(T(n,n,n))$ denote the rank of the $n \times n$ matrix multiplication tensor.
Let A=(a_{ij})_{1\le i,j\le 3}, \qquad B=(b_{ij})_{1\le i,j\le 3}, and let
We restart from the correct structural facts about matrix multiplication tensors and tensor rank, and avoid any assumptions about multiplicativity of rank beyond what is valid: subadditivity under dec...
We first restate the structure in a precise way consistent with the exercise.
Let $V$ be a $2$-dimensional vector space over a field $\mathbb{F}$ with basis ${e_1, e_2}$.