Questions on expression testing and manipulation through pattern matching and constructing efficient patterns.

learn more… | top users | synonyms (1)

42
votes
2answers
860 views

How is pattern specificity decided?

Mathematica has a notion of pattern specificity, which is a partial ordering on patterns. The rules (e.g. DownValues, ...
2
votes
1answer
56 views

Dropping rational coefficients

I have a list of expressions (they all are exact numeric quantities, not containing any variables), some of them have integer or rationals coefficients, or complex coefficients with rational or ...
0
votes
1answer
45 views

Specifying string patterns in a plain text

I need to extract three data, like that: (1.05, 1.37,A) from an imported list of plain texts: "... Syntax of parallax is : 'value quality [error] bibcode' value : parallax value quality : flag ...
9
votes
0answers
85 views

Strange result of DeleteCases in an association

The function DeleteCases can be used for associations, also with level specification. Here is an example where some values are associations: ...
9
votes
0answers
99 views

Confused by the opts : OptionsPattern[ ] pattern

I'm trying to make sense of the syntax in the clause opts:OptionsPattern[], as found in this standard "rule-based" (pseudo-)function definition pattern: ...
5
votes
0answers
240 views

Convert logical relational expression to / from disjunctive and conjunctive forms?

I would like to convert logical relational expressions in disjunctive form, e.g., $$(x \lt -1) \lor (-1 \lt x \lt +1) \lor (x \gt +1)$$ into conjunctive form, e.g., $$(x \ne -1) \land (x \ne +1)$$ ...
4
votes
0answers
82 views

Is there an elegant way of delaying evaluation of `A==B` when calling a function that uses this pattern

Suppose I wanted to define a number of functions that accepts expressions of the form: ...
4
votes
0answers
111 views

Why the flat f[x] is treated as ghostHead_[f[x]]?

While reading this answer I feel confused. If we do not care any specific detail of the original question, then ybeltukov's answer essentially makes use of the following fact ...
4
votes
0answers
198 views

Syntax error for optional pattern, but only in debugger

This expression (explained here by Leonid) evaluates fine unless Evaluation->Debugger is enabled: h[x : (_Integer) : 1] := x Syntax::sntxf: "x:" cannot be ...
3
votes
0answers
49 views

Error when combining Except, “*” and an additional character

Anyone knows why StringMatchQ["x", Except[{"1", "2"}]] StringMatchQ["x", Except[{"*"}]] StringMatchQ["x", {"1", "*"}] (* without Except *) all work as ...
3
votes
0answers
165 views

I am missing a function like HoldPattern

Temporary message: I am planning to edit this question, making the examples less confusing and by moving the things that are confusing to a separate question For any confusion about expressions that ...
2
votes
0answers
118 views

Is this a bug in NCAlgebra library?

In course of my work with NCAlgebra package for Mathematica, http://math.ucsd.edu/~ncalg/ , I encountered unexpected behavior of replacements. I am using ...
2
votes
0answers
337 views

NDSolve Issue with initial conditions

I am trying to implement a Poincare section for a gravitational movement on the plane $(x,y)$. Here is the code I wrote ...
1
vote
0answers
53 views

Why has FreeQ a quadratic complexity with high depth?

I am a little puzzled by the following test: ...
1
vote
0answers
33 views
1
vote
0answers
162 views

Crosscorrelation for nonperiodic signals

I want to detect patterns (of an absorption spectrum which is nonperiodic) with Mathematica automaticly. I have found CorrelationFuncion but as far as I understand, ...
1
vote
0answers
88 views

Symbolic and numeric calculations (and plots) simultanuosly

I use Mathematica to do a bunch of symbolic calculations (integrals, ...). This is good because I found that sometimes, if I plug in numeric values, Mathematica takes much longer. However, sometimes ...
1
vote
0answers
54 views

Hashing by Equals instead of SameQ

I have some numerical code involving complex numbers representing points on a plane. Some of these are equal but not identical, ie ...
1
vote
0answers
71 views

Function behavior based on Head

I'm figuring how to implement a function behavior based on the Head of its argument. I mean ...
1
vote
0answers
41 views

Matching Root[…] objects with patterns, unexpected hidden argument

I needed to write patterns that could distinguish between arbitrary-function and polynomial forms of Root objects, for example, ...
0
votes
0answers
71 views

Making a list of terms ordered by product order

I have some expressions f,g,h that are elements of a symmetric tensor algebra. The expressions are generated by a basis ...