An algorithm is a sequence of well-defined steps that defines in abstract the solution to a problem.

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4
votes
0answers
70 views

Implement a piecewise function elegantly and efficiently

Given that $$ g(x)= \begin{cases} max(x_{min},x-m) & 0.5x \leq max(x_{min},x-m) \\ 0.5x & max(x_{min},x-m)<0.5x<min(1,x+m) \\ min(1,x+m) & min(1,x+m)\leq 0.5x \end{cases}$$ ...
0
votes
1answer
49 views

timing series algorithm [on hold]

If we have a timing series t1,t2,t3.... and every timing point means an event. A time interval T is given. Once T is given, how to calculate the maximum event number happening in T? case A ...
22
votes
7answers
608 views

Alternative ways to implement a triangular recursion

Triangular recursions are a class of algorithms that frequently turn up in computational mathematics. These recursions are expressible in the general form ...
6
votes
3answers
226 views

Calculating integral by Romberg Algorithm

In my "Numeric Anasyis" course, I learned the Romberg Alogrithm to calculate the numerical integral. The Romberg Alogrithm as shown below: $$ ...
3
votes
3answers
76 views

Generating increasingly longer lists from a single list

I start with an array such as {{1,1},{0,1},{-1,1}}. (1) I want to create an array from this which replaces each array inside the array with 3 new arrays, one ...
5
votes
1answer
63 views

Enumerating tuples from a larger space such that all pairs of values are present at least once

I am trying to write a function that will accept a list of N lists and returns a list of N-tuples that represent all pairs of values from the original N lists at least once. To illustrate with an ...
6
votes
2answers
338 views

Pruning elements in an array based on the existence of similar elements in adjacent arrays

Imagine I have a series of particles floating around in $\mathrm{R}^3$, where, at any given time, particles can pop into and out of existence. Here, for some number of time points, $(t_1, \dots, ...
1
vote
1answer
113 views

How to create a Poincare disk type kaleidoscope in Mathematica?

Creating a Kaleidoscope in Mathematica is not a new topic at all, examples can be found from the links like: Wolfram reference and Wolfram demonstrations. My question is how to create Poincare disk ...
2
votes
1answer
129 views

Neighbourhood - Calculations

SeedRandom[0]; n = 5; (m = N @ RandomInteger[{1, 3}, {n, n}]) // MatrixForm result1 = MeanFilter[m, 1] // MatrixForm ...
48
votes
3answers
21k views

How to create a new “person curve”?

Wolfram|Alpha has a whole collection¹ of parametric curves that create images of famous people. To see them, enter WolframAlpha["person curve"] into a Mathematica ...
10
votes
5answers
573 views

How to deal with recursion formula in Mathematica?

In engineering problems, I am always seeing many recursion formula. For instance, In the book "The NURBS book", I discovered many recursion formula Fibonacci ...
2
votes
3answers
348 views

computing gaussian curvature

Can gaussian curvature K be computed from WolframAlpha or any other available Mathematica ...
9
votes
5answers
367 views
10
votes
2answers
158 views

Temporal database reconstruction in mathematica

<EDIT> after some internet research I found the database domain that deals with this kind of thing: Temporal Databases. I think my question therefore becomes how to reconstruct a temporal ...
2
votes
3answers
61 views

Reconstructing an expression [duplicate]

I have a nested expression like this one expr = Tan[Sin[Cos[x]]]; I can deconstruct it with ...
3
votes
2answers
202 views

A problem about recursion formula of deCasteljau algorithm

I use mathematica to realize the deCasteljaul algorithm $$\vec{P}_{k,i}(u_0)=(1-u_0)\vec{P}_{k-1,i}(u_0)+u_0\vec{P}_{k-1,i+1}(u_0)$$ The graphics that deCasteljaul algorithm generated as below: ...
5
votes
2answers
154 views

Graph expansion on Mathematica

Is there a way by which Mathematica can be given a graph as an input and be asked to find its expansion? Note: By "expansion" I mean the quantity called "isoperimetric number" or "Cheeger constant", ...
8
votes
3answers
292 views

Random Integer Sequences

I want to construct a random square matrix in the following manner: a) Three states [0 | 1 | 2] are repeated ...
14
votes
2answers
397 views

Better way to test that a matrix is upper-triangular?

Today, I got to thinking about how to test that a matrix was upper-triangular. So I had a try at it. Algorithm $\quad \quad a_{ij}=0 $ Or $i \leq j$ $\Rightarrow$ $True$ My solution is ...
9
votes
3answers
897 views

An inverted pyramid

I want to draw a pyramid approximately like this ...
11
votes
7answers
615 views

Splitting strings into letter keys and integers

I have strings of the following form: string = "ABC123DEFG456HI89UZXX1"; Letter keys of variable lengths are followed by (positive) integers. I want to get this ...
9
votes
5answers
704 views

Coalition Games

Suppose an election produces the following result: result = {{"a", 120}, {"b", 80}, {"c", 50}, {"d", 30}}; Letters are parties and numbers seats. To form a ...
18
votes
3answers
371 views

How to generate a blank crossword sheet?

I attempted to generate a blank crossword sheet. My method is by combining the rows and columns as shown on the graph below. However, some of the across and ...
9
votes
4answers
281 views

Replacing matrix values

I want to find the n largest values in a matrix and replace all others with zero. The solution I found uses ReplaceAll and becomes very slow as the size of ...
9
votes
2answers
168 views

Extracting values with multiple keys

I want to extract sorted data from a huge database based upon two (or more) keys in a very timely manner. Here is a reproducible toy example for two keys only: ...
4
votes
1answer
105 views

How to make a case insensitive sorted list and rename the file names of a given folder?

Suppose I had about 500 .JPG and .jpg files in my folder "c:\images\". How to ask ...
0
votes
6answers
195 views

How to build a game board [duplicate]

I have - rather lazily - constructed a chessboard like this: ...
12
votes
2answers
392 views

Implementing an algorithm for finding the largest circle that contains a single point in a set (and no other point)

This question concerns the implementation of an algorithm proposed by Rahul Narain on a former question of mine that was migrated to math.stackexchange: ...
0
votes
1answer
49 views

Speeding up ReplaceRepeated while truncating to desired order

I need to program in an algorithm that recursively makes algebraic replacements which leads to an utterly complicated algebraic function of $x$, but whose final result is only needed at fixed order in ...
6
votes
2answers
377 views

Counting the zeros in a factorial expansion [closed]

A number, as big as 1000! (! = factorial) is given. I need to find how many zeros are there in the number. I counted the no of terminal zeros by dividing 5, 25, 125, ... (untill fifth power < ...
16
votes
4answers
1k views

How to get actual triangles from DelaunayTriangulation[]?

The ComputationalGeometry package has a DelaunayTriangulation[] function. It returns a list of points connected to each point, ...
13
votes
4answers
666 views

“Indexing” a vector

I need to "index" a vector according to the first occurence of its distinct elements. I have written ...
1
vote
2answers
507 views

Faster way to test if an expression equals zero

I want to test if expressions (mix of variables, functions and numbers) are zero valued, as fast as possible, and PossibleZeroQ is sometimes very slow. One solution ...
19
votes
5answers
2k views

Mathematica Implementations of the Random Forest algorithm

Is anyone aware of Mathematica use/implementation of Random Forest algorithm?
10
votes
2answers
2k views

Machine learning. SVM algorithm

I want to work with machine learning in Mathematica. Are there any SVM algorithms implemented in Mathematica anywhere? Or any other algorithms for machine learning? With positive and negative database ...
0
votes
0answers
99 views

Spectral Clustering

I am interested in the following question: How is it possible to check whether an algorithm is working properly? However, this question is too general for the post and I'd like to restrict attention ...
8
votes
11answers
1k views

Ragged Diamonds

diamond[n_Integer] := Table[1, {#}] & /@ (Range[n]~ Join~Range[n - 1, 1, -1]) diamond[5] // MatrixForm How could a more functional, "tablefree", solution ...
1
vote
0answers
82 views

Creating a simple interactive app with CDF [closed]

I would like to implement an algorithm I have created using a (free) CDF document as interface. The idea is: The user has to give some input values (maybe through a sort of text box, if possible —a ...
0
votes
0answers
44 views

What Algorithm Does Mathematica use to Calculate Betweenness Centrality for Unweighted Graphs?

Recently asked this question http://math.stackexchange.com/questions/888369/betweenness-centrality-how-long-does-mathematica-take on the Mathematics SE. Does anyone know, as a follow up, what ...
8
votes
3answers
394 views

Find intersection points with V10

My question departs from this one: Find intersection of pairs of straight lines but now I want to find the points with the new V10 Region-functions. ...
3
votes
3answers
153 views

Multivariate Polynomial Manipulation

I have a large homogenous multivariate polynomial in, say, 5 variables $a,b,c,d,e$. As an example take the polynomial $$a^4+2abcd+a^2 b^2+e^4+cde^2.$$ Now I would like to replace $k$-th power of any ...
3
votes
2answers
242 views

All possible pairs of two items

I have 4 different items {1, 2, 3, 4}. I want to obtain all possible pairs of two of the items. I have written: ...
-1
votes
3answers
188 views
13
votes
6answers
418 views

Partitioning an integer into $k$ equal parts

Say I have an integer $M$. Is there a one-line command to create a partition of $M$ into $k$ integers s.t. the difference between any two integers is as small as possible? For example, with $M = ...
8
votes
8answers
704 views

Replace interior of matrix with zeros

I have f.e. the following square matrix: ...
16
votes
11answers
1k views

Efficient way to build a certain quadratic matrix

For odd n I'm looking for a short and swift way to construct with (f.e.) n = 3 n = 11 ...
1
vote
5answers
242 views

Write a number as the product of its two largest divisors

For even n >= 10 && n <= 98 I want to write n as the product of its two largest divisors (excluding ...
1
vote
0answers
98 views

What's a non-trivial Mathematica program involving conscious choice of stack vs. queue data structure?

In a typical computer science algorithms course, much attention is given to the discussion of queues vs. stacks as a data structure programmers need to consciously choose from to achieve algorithmic ...
39
votes
1answer
1k views

How to construct a treemap using non-rectangles?

I've written the standard version of a tree map (a graphic that shows nested data) and I'm looking to improve on this layout by switching to different types of polygons or perhaps circles. Can anyone ...