Tagged Questions

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

66 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 ...
125 views

Logical AND of multiple patterns

Mathematica provides an equivalent for "logical OR" when pattern matching, using Alternatives or the infix | operator. For ...
96 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: ...
150 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: ...
267 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., $$(x \ne -1) \land (x \ne +1)$$ ...
37 views

Pattern match Shortest BlankNullSequence in SequencePosition

Apologies if this has an answer somewhere but I can't find it. From the examples for SequencePosition we are shown that ...
55 views

How to get f[x] to match with f[c_., x] when OneIdentity doesn't match

After setting: SetAttributes[f, OneIdentity] Default[f] = 1; We have the following successful matches: ...
118 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 ...
265 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 ...
178 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 ...
46 views

Is pattern matching just systematic guessing and checking?

How does the pattern matcher work? how does it match this example? f[3, h[4]] /. f[x_, z_[y_]] :> {x, y, z} My guess is that the pattern matcher collects all ...
44 views

Replacement rule for summation with Kronecker delta

I want to perform some symbolic computations in index notation, without explicit reference to sums, so that in expressions of the type f[i,j]g[j,k] summation over <...
65 views

Good coding for integral substituions

This question is aimed at improving both my coding and my understanding of MMa's capabilities. A lot of my code is still hacks and workarounds for things I don't know how to do properly. I want to ...
439 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 ...
82 views

How to “INJECT” with holding Evaluation, specifically into a WhenEvent

I am importing a set of differential and stochastic equations from an external package, and want to use Mathematica to analyse this. I am struggling building the set of equations that I can use with <...
71 views

Unexpected result when trying to match against the arguments of Times

Consider the following question: ...
58 views

Why has FreeQ a quadratic complexity with high depth?

I am a little puzzled by the following test: ...
45 views

FirstPosition returning an error message together with the correct answer

I have the following code: ...
254 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, ...
66 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 ...