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2019-06-25 15:55:24 +0100 | asked a question | 3-d bezier-path made thick I want to draw a $3$-dimensional bezier path with thickness=5 instead of the default value 2, using the code
recommended in the manual. It seems however, that the thickness does not change. What do you suggest? |
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2018-06-06 16:12:15 +0100 | asked a question | More problems with general power of a matrix Even though in version 8.2 the code for the general power of a matrix has been improved (c.f. question 41622), it still doesn't work in some cases, as i.e. this singular, diagonalizable matrix shows. Concerning the remark in trac ticket 25520: Why not defining $0^x=1$ for $x\in {\bf N}$, which seems reasonable, since the number of functions $\emptyset \to \emptyset$ is 1? |
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2018-03-31 21:49:26 +0100 | asked a question | Combinatorial Species of Phylogenetic Trees I would like to study the combinatorial class ${\cal H}$ of labelled phylogenetic trees, defined as rooted trees, whose internal nodes are unlabelled and are constrained to have outdegree $\geq 2$, while their leaves have labels attached to them. According to Flajolet, Sedgewick: Analytic Combinatorics, p. 128, this class satisfies the recursive specification $${\cal H}={\cal Z}+\mbox{Set}_{\geq 2}({\cal H})$$ I defined their species $H$ by the code The number of labelled structures is given by the integer sequence. In particular I tried to calculate (for a small cardinal number)
using the following code: Only 2. seems to work. If my code ist correct, I wonder if some of these (i.e. composition species) are not implemented and when (whether) they will be. |
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2018-03-22 22:51:10 +0100 | edited question | Bug in general power of a matrix The code to question 35658 gives a wrong answer i.e. for the matrix Where can I find an improvement? For $k\in {\bf N}$ the $k$-th power of a matrix $A\in {\bf R}^{n\times n}$ satisfies by definition the recursion $A^{k+1}=A*A^k$ and the initial condition $A^0=I$. Substitution of $k=0$ and $k=1$ should therefore give the identity matrix $I$ resp. the matrix $A$. The following live code does (currently) not give the expected answer. Btw: One of the M-programs gives the correct answer. |