# Tagged Questions

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

67 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 ...
64 views

### Collect partial derivatives and rewrite them with delta/nabla

Ultimately, I wish to get the higher generalized product rule for Laplacian. That is, we have $\Delta(fg)=f\Delta g+2\nabla f\cdot\nabla g+g\Delta f$ but what is $\Delta^n(fg)$? I am tying to guess ...
80 views

### What has changed in pattern matching functions with the Orderless attribute?

In making an attempt to answer this question, we ran into a version-dependent pattern-matching issue. An extended discussion in the comments transpired, and some inconsistencies arose. Consider the ...
130 views

### Logical AND of multiple patterns

Mathematica provides an equivalent for "logical OR" when pattern matching, using Alternatives or the infix | operator. For ...
153 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: ...
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: ...
268 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., $$(x \ne -1) \land (x \ne +1)$$ ...
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### Possible bug with KeyValuePattern and Optional

I expect to get 0 on every line of output of this: ...
38 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 ...
56 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: ...
119 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 ...
271 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 ...
29 views

### Generating a list of random numbers that follows a pattern

I'm a beginner to Mathematica. I'm writing a code to design a 4-bar linkage mechanism that traces a path in 2D space. I got the modelling done right, now I'm writing my own implementation of a genetic ...
64 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 ...
180 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

### 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 <...
66 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 ...
444 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: ...
262 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, ...
67 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 ...
88 views

### Function behavior based on Head

I'm figuring how to implement a function behavior based on the Head of its argument. I mean ...