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tamnd's digital brain — notes, problems, research
43815 notes
Let each available area be represented by a node $P$ with fields $\text{LOW}(P), \text{HIGH}(P), \text{SIZE}(P)=\text{HIGH}(P)-\text{LOW}(P)+1,$ and let all free areas be stored in a balanced binary t...
In MIX arithmetic, the instruction `DIV d` interprets the concatenation $AX$ as a single signed integer formed with $A$ as the high-order word and $X$ as the low-order word.
We construct all values for $V_t(8)$ using a single consistent method: an optimal 8-element tournament followed by explicit optimal selection in the induced comparison structure.
The previous solution fails because it introduces unnecessary hierarchical structure that does not preserve the global constraint from Exercise 5.
We give a complete corrected proof by isolating the precise mechanism that guarantees both row and column inequalities during each bumping operation, without circular reasoning.
Let $N$ keys be stored in an $M$-ary trie under the uniform random model in which each digit of each key is independently uniformly distributed in ${0,1,\dots,M-1}$.
**Exercise 5.
Let a variable-length key $K$ be a finite sequence of MIX characters $K = c_1 c_2 \dots c_\ell,$ where each $c_i$ is an element of a fixed alphabet of radix $r$ (for MIX, typically $r = 64$ or $r = 10...
The previous solution fails because it never reconstructs the _actual performance quantity in TAOCP’s striping model_.
The previous solution fails because it invents structure and singularities instead of deriving them from the actual expression in (18).
In the modified Algorithm D, step D3 sets c\leftarrow0, and each time step D4 is entered, the counter is first increased:
Let $n = Mb$.
Let a file consist of $N$ records with totally ordered keys.
We correct the analysis by rebuilding the argument from the actual insertion model and then performing a genuine worst-case optimization over all valid full nodes and all valid splits.
**Exercise 5.
We restart from the correct structure of a 4-tape polyphase merge.
The flaw in the previous solution is that it never uses the data in Tables 3 and 4.
Let $A$ denote the null pointer used in Algorithm T.
We correct both parts, addressing the missing rigor in Algorithm D and completely rebuilding the Patricia argument using a valid global construction.
For each pair $(j,i)$ with $j<i$, step C4 increases exactly one of `COUNT[j]` or `COUNT[i]`.
We restart the construction in a fully TAOCP-consistent form by defining a single recursive deletion procedure in which every descent step is preceded by an invariant-preserving repair.
Let $B_{n,h}$ denote the number of AVL (balanced) binary trees with $n$ internal nodes and height exactly $h$, and B_n=\sum_{h\ge 0} B_{n,h}.
Let $C(N)=\log_b N$ for a constant $b>1$ to be determined.
Let $m=7$.
Let a FORTRAN identifier be a string $K = c_1 c_2 \dots c_n$ with $1 \le n \le 10$, and let the proposed hash function be h(K) = \text{leftmost byte of } K.
(a) The permutation $376981452$ has the disjoint cycle decomposition (1\,3\,6\,4\,9\,2\,7)(5\,8).
Shar’s method in this exercise is the standard binary search method on an ordered table.
Let $P = T-1 \ge 2$.
Let $K$ be the search argument, and assume it is represented as a sequence of characters ending with the blank symbol used in Algorithm T.
Let the initial distribution place $S$ runs onto $P$ input tapes for a $P$-way merge under Algorithm F in Section 5.
Let H_N^{(\theta)}=\sum_{k=1}^{N} k^{-\theta}, \qquad \theta \neq 1.
Let $G_n$ be the $n$-cube with vertex set $\{0,1\}^n$.
The reviewer is correct that the previous solution replaced Program F’s frequency model with an unjustified uniform-visitation assumption.
Let $F = \mathrm{GF}(2^n)$, and let $a \in F$ be an element of order $n$.
Let $N>1$ be arbitrary.
The flaw in the previous argument is not the linear algebraic part but the missing derivation of the transition rule from the definition of the perfect Fibonacci (perfect polyphase) distributions in (...
Let $N=12$.
The previous proof failed because it incorrectly treated reachability in a general DAG as if it could be incremented only locally per comparison, and then incorrectly decomposed two dependent costs as...
Let $b_1 b_2 \dots b_n$ be the inversion table of the permutation $a_1 a_2 \dots a_n$.
Let N(a,b,c) denote the number of permutations of the multiset
Working
Let $R_1,\dots,R_N$ be the file and let $d(K_i,A)$ be the distance from record $R_i$ to the given argument $A$.
Let Algorithm S be the full sequence of insertions described in Algorithm I applied successively, terminating with a tableau $P$ and a final added position $(r,s)$ determined at the last insertion ste...
We work in the model where a _stage_ consists of a set of pairwise disjoint comparisons, and all comparisons in a stage are executed simultaneously.
No.
The root node compares $K_1$ and $K_2$.
Algorithm C still works if $i$ varies from $2$ up to $N$ in step C2 instead of from $N$ down to $2$, because the comparisons made in step C4 depend only on the relative ordering of $K_i$ and $K_j$, no...
Let $N$ keys be inserted in random order into a binary search tree generated by Algorithm T.
Let $A_{i,j}$ be defined by Eq.
The core mistake in the previous argument is the attempt to manufacture a per-level varying radix structure from tape-role behavior.
We compare cascade sorting on three tapes (Algorithm C) with polyphase merging on three tapes (Algorithm 5.
Let $T$ be a binary search tree with cost C(T)=\sum_{i=1}^n p_i\,\mathrm{depth}(k_i)+\sum_{i=0}^n q_i\,\mathrm{depth}(d_i), where all $p_i,q_i\ge 0$ and $p_n=q_n=0$.
Let a weight-balanced tree be a binary tree in which there exists a fixed constant $0 < \alpha \le \tfrac{1}{2}$ such that for every internal node $v$ with subtree size $n(v)$, its left and right subt...
**Corrected Solution to Exercise 5.
Let $A_n$ be the expected cost of an $M$-ary digital search tree built from $n$ random keys, and let $P(z)$ be its Poisson transform.
Algorithm R performs a sequence of $p$ distribution passes, each pass grouping records into $M$ FIFO queues according to a single digit $a_{p+1-k}$.
Let f_p(z)=z^p - z^{p-1}-\cdots-1.
We restart from the actual stochastic structure of tertiary clustering and keep track of the dependence that was incorrectly removed in the previous solution.
Let the selection algorithm be modified so that the input is partitioned into groups of 5 instead of groups of 7, and the median-of-medians is used as the pivot exactly as in the proof of Theorem L.
Let $A_i(n)$ denote the minimum transmission cost (external path length) among all merge trees with $n$ leaves, under fixed parameters $a$ and $b$ as in Section 5.
Batcher’s merge-exchange method is not stable.
Let $S_N = d_1 + d_2 + \cdots + d_N$.
Start from Eq.
The flaw in the previous solution is that it replaces Algorithm U’s interval invariant with a “reachability” heuristic.
Let $T_n$ be a digital search tree constructed by Algorithm D from $n$ keys $K_1,\dots,K_n$, where the keys are independent infinite binary sequences with each bit independently $0$ or $1$ with probab...
Let $H$ be a matrix whose rows are hash functions $h : \mathcal{K} \to {0,1,\dots,M-1}$, and whose columns correspond to keys.
The previous solution fails because it ignores that block placement is constrained by the _run structure of the merge schedule induced by the Gilbreath principle_, not by the index order of the input...
Let F(z)=\frac{p(z)}{q(z)}, \qquad G(z)=\frac{p(z)}{q(z)^2}.
Let $T$ be any comparison decision tree for merging $A_1<\cdots<A_m$ with $B_1<\cdots<B_{n+1}$, and let its height be the number of comparisons in the worst case.
Let \pi = (1,2,5,3,7,4,8,6,9,11,10,12).
Let $N = 365$ and let $n$ be the number of people.
Let ${F_n^{(p)}}_{n\ge 0}$ denote the $p$th-order Fibonacci numbers defined in Section 5.
A $t$-ary tree is a rooted ordered tree in which each internal node has at most $t$ children.
The previous argument failed because it replaced both the definition of $s(n,\alpha,y)$ and Abel’s identity with unverified variants.
We restart from a faithful snowplow model of replacement selection and avoid any per-record attribution.
Working
**Corrected Solution for Exercise 5.
Let $t > 2$ and $k > t$ be integers.
**Corrected Solution: Exercise 5.
The error in the previous solution is not cosmetic.
Algorithms 6.
Let the hash table be initially empty and let linear probing be used for collision resolution.
Let floors $p<q$ satisfy $g_q>p+2$, $u_p>0$, $u_q>0$, and $u_{p+1}=\cdots=u_{q-1}=0$.
The errors in the previous solution stem from two issues: (i) failure to verify that the transformation “descending run = apply $x \mapsto 1-x$” preserves the structural hypotheses of Theorem K at the...
Let the table size be $M$, with $n$ stored keys and load factor $p=n/M$.
The exercise statement is incomplete.
Let f_p(z)=z^p-z^{p-1}-\cdots-z-1,\qquad p>2, and define
Let $T=6$ and $P=5$.
The argument fails because it replaces the algorithm of Exercise 25 with an unrelated Touchard model and then manipulates that model without any link to run termination.
Let Algorithm B denote the standard binary search of Section 6.
The flaw in the previous argument is real: the insertion point cannot depend on the unknown divergence index $d$, so any attempt to define it during the initial search is circular.
Let keys be infinite binary sequences generated by independent unbiased bits.
**Exercise 5.
Let $R_1,\dots,R_N$ be the records, and let their final order after two-way insertion be determined as in Table 2, where each new record is inserted either to the left end or the right end of the curr...
The changes preserve correctness.
Let $B_h$ denote the number of balanced trees of height $h$, and define $C_h = B_h + B_{h-1}$.
Let $T(6)$ denote the minimum depth of a sorting network on 6 inputs.
The search for $613$ proceeds from the root by repeated comparison with the keys in each visited node, following the rightmost pointer at each step since $613$ exceeds every key encountered in Fig.
We restart from the actual structure of the defining equation (15) and avoid introducing any artificial kernel.
Let $\theta \in (0,1)$ be irrational, and let the sequence of points ${n\theta}$ be inserted into $[0,1]$ as in Theorem S of Section 6.