Questions tagged [pattern-matching]
Questions on expression testing and manipulation through pattern matching and constructing efficient patterns.
1,473
questions
7
votes
2
answers
327
views
0
votes
1
answer
68
views
PiecewiseExpand fails to address assumptions
PiecewiseExpand seems to ignore more complex assumptions. Here's an example:
...
- 633
1
vote
0
answers
57
views
DigitQ, LetterQ, UpperCaseQ, LowerCaseQ on empty string
Is this a bug or I am missing something?
#[""] & /@ {DigitQ, LetterQ, UpperCaseQ, LowerCaseQ}
...
- 9,568
3
votes
1
answer
110
views
Switch with string patterns
I'm trying to use Switch to process lines from a text file. I know that
StringMatchQ["abc", "a"~~___]
...
- 133
3
votes
1
answer
125
views
Pattern matching vs. condition in a function
I'm trying to learn stuff from pattern matching but I found sometimes pattern matching does not work as I expected. Could anyone explain why the below outputs are not same? Thank you.
And could anyone ...
- 31
0
votes
1
answer
40
views
Transform a list of delayed rules with conditions to a new list of delayed rules
I have a list of rules that implement some abstract algebras, for instance, that of the Pauli matrices,
...
- 513
2
votes
1
answer
51
views
ToString[n] in pattern replace does not take the value of n
I would like to convert expression to C++ code.
Based on these demostrations.
...
- 197
2
votes
1
answer
51
views
Is it possible to ask Mathematica to give/find this largest (absolute value) argument of $\cosh$ in the expression?
I have the expression exp in terms of Cosh functions:
...
- 137
2
votes
1
answer
48
views
How to apply a transformation to a total derivative?
I want to transform total derivatives into normal derivatives:
Dt[r, t] == -r*Dt[v, x] - v*Dt[r, x] /. Dt[f_, s_] :> D[f[x, t], s]
To get:
...
- 363
5
votes
1
answer
201
views
How to Replace 'delta t' with 'a' in Mathematica Without Affecting Separate Instances of 'delta' or 't'?
In Mathematica, how can I replace instances of delta t in an expression with a, while keeping instances of ...
- 215
6
votes
1
answer
304
views
Why does this pattern not match?
Why does the following match?
MatchQ[HoldPattern[f], HoldPattern[_]]
True
But the following does not:
...
- 47.1k
7
votes
6
answers
483
views
Apply function to all first arguments of a nested list of rules
Currently, I have a nested list of rules of the form
lst1={1->a,2->{3->c,4->d,5->{6->f,7->{8->h,...}}}}
(where I don't know the length of ...
- 323
1
vote
0
answers
98
views
Optimize grouping of list of lists by elements
I have a sorted list of lists of size ~200,000 x 3. The data are such that the first element of each triplet loops through i = 1, 1.1, 1.2, ..., 199.9, 200, and for every value of i, the second ...
- 11
1
vote
2
answers
88
views
How to break a term in its individual factors?
I have some algebraic term that looks like this,
Conjugate[Subscript[u, 1, 1]] Conjugate[Subscript[u, 2, 1]]
\!\(\*SubsuperscriptBox[\(u\), \(1, 1\), \(2\)]\)
$$...
- 11
1
vote
1
answer
81
views
Applying matrix commutation rules
I want to symbolically replace occurences of matrix terms such as $zAB-zBA$ with $zC$, where $z$ is a number. This works as expected:
...
- 13
2
votes
3
answers
136
views
Replace only some instances of a symbol in an expression depending on what it's multiplying it
I have an expression of the type
expr = k*a + j*a + a*f + a*g + h
And I would like to set a=0 but ONLY if it's NOT multiplied ...
0
votes
2
answers
126
views
Einstein summation pattern matching
I have an expression of the form
expr = $(A\cdot B)\;(C\cdot D)\;(F\cdot G)$
where $A, B,C, D, F, G$ are all vectors. I would like to use Einstein summation convention for each dot product and then ...
- 95
5
votes
2
answers
207
views
Crafting a replacement rule to convert derivatives to finite differences
I need to construct a replacement rule to replace (first) derivatives with centered finite differences. What I've got so far is
...
- 19.5k
2
votes
2
answers
60
views
MatchQ strange behavior
While checking for a pattern I came across this test:
MatchQ[-A.Grad[Subscript[f, 1, 1],k], ___.Grad[Subscript[f, x_,x_],_]]
which returns ...
- 95
5
votes
6
answers
160
views
Generate all possible lists of integers that match a pattern
I have a pattern defined using variables: {a,b,a,b} and I want to generate all possible instances of this list where each variable ranges from 1 to n, and each ...
- 139
0
votes
0
answers
36
views
Commutator for Solving Coefficients in a Hamiltonian
I am relatively new to Mathematica but I understand the basics.
I want to solve for coefficients by commutator constraints and I have problems implementing the commutator. The setup is the following:
...
- 1
1
vote
2
answers
83
views
Pattern matching for an algebraic equation
I have question related to pattern matching of a complex algebraic equations. If I am about to extract certain terms from an algebraic expressions that contains mixture of terms $\nabla_\gamma 𝑓_{\...
- 95
1
vote
1
answer
81
views
Simplifying algebraic expression using pattern
Given the following expression
expr = x Cos[y] + x^(2 y) + x y + Sin[x^2 z Cos[y]];
I would like to achieve the following output:
...
- 95
0
votes
1
answer
42
views
Dealing with commutative, noncommutative variables and patterns with NC Algebra
I use NC ALgebra to deal with polynomials in non commutative variables ei and fj. The eis do not commute with themselves, the fjs do not commute with themselves, but the ei commute with the fjs. So e2 ...
- 11
5
votes
2
answers
154
views
Element position and repetition syntax
Please give me some advice.
There is box[x,y] and this is consisting of {{a1,{b1,c1},d,e},{a2,{b2,c2}}} elements.
For example, box[x] is list like this.(and Sometimes there is empty set)
...
- 294
0
votes
1
answer
50
views
Simplify expression with function with symmetric arguments
I have the following expression
$$ \frac{1}{2}\partial_\nu\partial_\xi h^{\nu\xi}-\frac{1}{2}\partial_\nu\partial_\xi h^{\xi\nu}+ \partial_\xi\partial_\nu h^{\xi\nu}- \frac{1}{2}\partial^\nu\partial_\...
- 231
1
vote
2
answers
100
views
Replacing Kronecker delta times expression with the expression with inserted index
Consider the following symbolic expression:
expr = f[a,b]*g[c,d]KroneckerDelta[a,m]KroneckerDelta[d,k] + KroneckerDelta[a,p]f[x,a]+const
Could you please tell me ...
- 4,632
3
votes
2
answers
187
views
Replace a column/row of a matrix under a condition by a random number
Lets say there is a matrix of the form:
matrix = {{1,2,3},{4,5,6},{7,8,9}}
I want to replace the elements of the last column, if they are larger then zero, by the ...
- 427
1
vote
1
answer
64
views
Can not get OptionValue with SetDelayed variable
ClearAll[foo1];
foo1[OptionsPattern[]] := Hold[OptionValue[""]][[1, 1]]
foo1[]
gives function name
foo1
But
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- 16.9k
1
vote
0
answers
49
views
Replacing a symbolic fraction in a matrix by pattern matching
I have the following 4x4 symbolic matrix
...
- 429
4
votes
2
answers
123
views
Selecting sublists from a ragged array of lists of strings
A ragged array of strings with a mix of sublists is processed to output some sublists and not others.
The sublists to output have a date, data, and information; in no particular order.
The information ...
- 51
1
vote
1
answer
69
views
How to collect products of DiracDelta functions?
After taking a FourierTransform, I have the following expression containing multidimensional products of delta functions (what I am actually working with is far longer than this excerpt):
...
- 113
4
votes
3
answers
211
views
Find shortest subsequence
We will deal with arrays of chars, but not strings!
Let we have the next three arrays:
...
- 1,197
2
votes
1
answer
63
views
How to match all zero valued cashflows?
I have a function that needs to identify cashflows with zero value:
MatchQ[Cashflow[{{0,0},{1/2,0.`},{1,0.`},{3/2,0.`}}],Cashflow[{{_,c_/;Chop[c]==0}...}]]
The ...
- 9,113
0
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0
answers
40
views
Is this behaviour of pattern ordering of OptionsPattern stable and documented? [duplicate]
My version is 13.2. This behaviour of OptionsPattern together with `` is extracted from some complicated functions.
Motivation
<...
- 2,208
5
votes
2
answers
89
views
Is there a difference between a (general) pattern and a string pattern?
I have a list myList that contains several strings. I wish to use Position to find the positions of strings in ...
- 10.4k
1
vote
3
answers
67
views
Functions with a greek, subscripted argument [duplicate]
I am working on a problem with a lot of (greek) variables and it makes sense to sub-script them. Some of them must appear in functions and I am having trouble using greek, subscripted variables ...
- 187
0
votes
1
answer
69
views
Finding a pattern an exact number of times and excluding patterns
I have a list of expressions which are multiplications of different types of objects.
The question is broadly about how I can look for a pattern an exact number of times and exclude patterns from the ...
0
votes
0
answers
55
views
Using Count[] on a numerical list with approximate numbers
I have a matrix, SpinOp, for which I obtain the Eigensystem using {evalSpinOp,evecSpinOp} = Eigensystem[SpinOp]. I need to ...
- 431
5
votes
0
answers
84
views
Using Cases to select expressions from a list
I am using v12.2.0 on Win7-x64. I want to use Cases to select the Times and Plus cases from ...
- 41.4k
0
votes
1
answer
26
views
Given input expressions, extract the base and make it as a list
Given input expressions, I want to extract the function and again extract its element.
For example, given my input
...
- 801
1
vote
2
answers
67
views
Assigning a value to a functions argument
I´m struggeling now a few hours on a very basic problem. I want to assign the value 0 to variable i, if i has another value, then it should be changed to 0 in the function.
Function
...
- 33
2
votes
0
answers
43
views
2
votes
2
answers
80
views
Pattern match and then replace the argument
I've want to replace the pattern, say I the arbitrary function $o$ that takes one argument, now, if the two of these function meet in a expression, one with some arugment $B$ and the other with the ...
- 698
1
vote
0
answers
72
views
9
votes
6
answers
725
views
Can I tell DeleteCases not to delete function arguments?
Given list = {1, 2, f[3, 4], {5, {6, g[7, h[8, 9]]}}, {f[10], 11}};
I want to get
{f[3, 4], {{g[7, h[8, 9]]}}, {f[10]}}
just ...
- 5,562
8
votes
1
answer
130
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Replacing 2D Patterns in 2D Lists | Markov Programming Language
Recently I came across with a probabilistic programming language where programs are combinations of rewrite rules - Markov Junior
I think it is quite interesting to try out implementing some features ...
- 1,177
1
vote
1
answer
76
views
Reducing roots of power sums
Often I encounter expressions like for example
Root[ 1 - # + #^2 - #^3 + #^4 - #^5 + #^6 &, 3 ] or
...
- 1,470
2
votes
2
answers
114
views
Remove sublists with duplicate elements within
I have this list
DeleteDuplicates[Sort[#] & /@ Tuples[Range[4], 3]]
which gives me
{{1, 1, 1}, {1, 1, 2}, {1, 1, 3}, {1, 1, 4}, {1, 2, 2}, {1, 2, 3}, {1,
2, 4},...
- 426
2
votes
1
answer
77
views
Pull out numerical factors from the argument
I'm trying to define a function that is distributive over Plus and pulls out the numerical factors from the argument:
...
- 966