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

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4
votes
4answers
159 views

Express block matrix in terms of matrix basis

I'm trying to construct a function that returns the multiplication table of a matrix Lie algebra. Assuming a basis of matrices, my definitions: ...
4
votes
2answers
218 views

Assumptions with patterns

I want that Mathematica assumes every symbol like Subscript[s,i] to be evaluate as a real and positive number. I have tried ...
4
votes
3answers
212 views

How to highlight the elements in a list that match a pattern?

For example, {{1,2,3},{1,2,3,1,2,3,4,5}}with pattern {1,_,3}is transformed to ...
1
vote
2answers
116 views

Is there a way to search for Arithmetic Progressions in a list?

If you have a list of integers is there a way of searching that list to see if there is a trend of Ax+B in the list? Not using all of the numbers, just seeing what trends like that are embedded in a ...
8
votes
2answers
332 views

Matching pair of numbers {a,-a}, where a is numeric

Imagine you have a list of pairs of numbers, such as {{2,-2}, {1,5}, {1,-3},{-3,3}} The task is to reduce the given list to a list of pairs of type ...
6
votes
1answer
114 views

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

Bug introduced in 5 or earlier and persists through 10.4.1 Anyone knows why ...
2
votes
3answers
147 views

DeleteDuplicates in a list of 2-tuples under condition

Having a list of 2-tuples, I would like to delete such 2-tuples that have 0 at second position, but only those, whose first element is not unique in the list. E.g. ...
1
vote
2answers
140 views

How do I use ReplaceAll to replace strings of a specified form?

Why is "Xabcde" /. "X" ~~ e__ -> e "Xabcde" and not "abcde"
1
vote
1answer
49 views

Matching x,y,z,2

I have a list of integers; I would like to replace anything of the form $x,y,z,2$ in such a list with $x+1, y+1, 0, 0$. The problem is that the $2$ may appear at the front, or in the first three ...
5
votes
3answers
185 views

Better output for NonlinearModelFit “ParameterTable”

The Standard table fo parameters of NonlinearModelFit is obtained from NonlinearModelFit[{{0, 1}, {1, 2}, {3, 3}}, a + b*x, {a, b}, x] %["ParameterTable"]] I ...
10
votes
2answers
332 views

Why can I not replace a Dataset using a rule?

Simple replacement of a Dataset object does not seem to follow the expected behavior... Dataset[{}] /. _Dataset->1 Returns the empty Dataset not 1 as I would ...
0
votes
1answer
53 views

Selecting from a list [duplicate]

OK, I know this must be a simple problem, but right now I'm just stuck and need some advice with this :). I have the following list: ...
0
votes
3answers
72 views

ReplaceRepeated made a single replacement where I expected multiple replacements to be made

This seems like a very simple action: {a, b, c, d, e, f} //. {r___, x_, y___} :> {r, 1, y} but it replaces only the first element giving ...
7
votes
4answers
474 views

Strange answer from StringReplace

I have a list of strings and I would check if there is an empty string element, that's "", because I need to replace it with a "0". I try the following ...
1
vote
0answers
44 views
1
vote
1answer
41 views

How do I match all the subscripted terms in Times?

Suppose I have an expression: $W = A_{i,p,q...}\,\, a_ia_ja_ka_l...$, where $A_{i,p,q...}$ is an expression that does not depend on $a$, the indexes $i,j,k,l,p,q...$ are integers and all the integers ...
2
votes
1answer
91 views

How to make Simplify/Expand work in patterns?

I am trying to calculate deriv of a complicated function and store the values for reuse. But the FullSimplify in my definition doesn't seem work all the time: ...
2
votes
2answers
173 views

Extracting numerical coefficients from an expression

I have very large expression and I want to extract and sum up all the numerical coefficients which multiply the summands. For example, expr = x + 2*y + 3*z*w ...
3
votes
3answers
189 views

Change matrix elements at specific locations?

Let's say I have an array a={{1,2,3}, {4,5,6}, {7,8,9}} I want to have all elements along the diagonal multiplied by 2. ...
2
votes
2answers
163 views

Can a pattern examine all partitions of a sequence?

Say I have a list: {a, b, c, d}. I'd like to check that the list has some partition, say {{a, b, c}, {d}} such that all the elements of the partition satisfy a ...
0
votes
1answer
135 views

Replace elements that match pattern

I am using pattern matching to identify elements in a list to be replaced. How can I supply a list of patterns to match and replace all elements in the list that match the pattern? The problem I have ...
2
votes
1answer
100 views

Removing characters from non-strings

I have a large list of lists that contains mixed data, some real, some strings. The lists are of various lengths and depths. Some of the real data values have an asterisk appended to them, e.g.: <...
6
votes
6answers
522 views

Determine if all the zeros in a list occur at the end

I have a collection of (short) lists of nonnegative integers. For each, I would like a predicate that decides if all of the zeros in the list appear at the end. For example, ...
5
votes
1answer
112 views

Compare tree structures in mathematica

Since Mathematica expression is basically a tree structure, I would like to perform tree structure comparison with certain restrictions, for instance that the identity of nodes on the same level be ...
9
votes
3answers
131 views

Pattern matching with Complex. Feature or a bug?

fixed in 10.1 (windows) I have run into some strange behavior while doing some pattern matching. First, this works as expected: ...
0
votes
3answers
77 views

How to create a general expression for an integer derivative?

I need MMa to return a general expression for the jth derivative wrt v of v^n. This didn't work: ...
0
votes
1answer
79 views

How to use pattern matching for integral identities?

I have an unknown pdf f[x], and I need to express integrals involving f[x] as expansions of the moments of f[x]. For example: ...
7
votes
2answers
275 views

How can I construct a recursive pattern guard?

I am modelling binary trees in Wolfram Language by writing them as three-element lists, like so: binTree = {nodeVal, leftChild, rightChild}. It does not yet matter ...
5
votes
5answers
182 views

Isolating cross terms

I have a set of expressions that contains terms like $\frac{1}{(x + a + b)(c+d)}$. I would like to simplify the denominator so that products of $a,b,c,d$ are dropped, but $x c$ and $x d$ are kept. ...
0
votes
2answers
72 views

FilterRules with pattern for name [duplicate]

I have a list of rules and I want to filter it using a pattern for the initial string representing the name of the rule. So that in the example below it filters linearBool even if it is called "linear"...
2
votes
1answer
122 views

Odd behavior matching powers of pi

I have a long list of generated values from which I want to remove "weird" ones like Sin[Sin[1]] and Pi^2/4. However, trying to ...
4
votes
1answer
130 views

Output function control and manipulation for efficient computation [closed]

I have taken note of a similar post related to modifying function parameters. I tried to adapt Kuba's solution to this post but I can't get it to work. I will illustrate my problem using a similar ...
4
votes
1answer
254 views

Pattern matching multiple symbols names and powers

Seemingly a relatively simple problem, I can't seem to find a solution... I want to build a pattern that will match any symbol whose name starts with V, and is elevated at any power. Something on the ...
1
vote
1answer
61 views

How to modify the output result of an evaluation

For ease of notation, I have defined a function, $f$, that defines the permutation of Bosonic particles such that it has the following properties (the form of $f$ is irrelavent for this question): $\...
8
votes
3answers
314 views

Why these ways of defining a function with variable number of arguments fail?

First: I know about the correct way to define a function with variable number of arguments: Clear[f] f[s__] := Plus[s] f[1, 2, 3, 4] (* 10 *) BUT I ...
0
votes
2answers
83 views

Keep exponents separately

I have the following expressions $g^{ab+cd+...}$ or in the full form Power[g,Plus[Times[a,b],Times[c,d],...]] How to convert this expression into ...
4
votes
3answers
145 views

Extracting subscripts and superscripts

Suppose I have several types of expressions (in some random order) of the form Power[Subscript[g, a], μ] which is $g_a{}^\mu$ ...
10
votes
1answer
404 views

How to visualize pattern matching process?

I want a function that does the same job like ReplaceRepeated, and can make the matching process visible. I searched the Internet but didn't find any existing code ...
3
votes
4answers
295 views

How to search for patterns to find the positions of prime numbers

I have a summation which yields a prime number at each location there is a 2, and I do not know how to search for the 2's. ...
7
votes
5answers
748 views

Calculating weird numbers

A weird number is a number such that the sum of the proper divisors (divisors including 1 but not itself) of the number is greater than the number, but no subset of these divisors sums to to ...
5
votes
3answers
201 views

How can I improve NumberString?

I would like to test strings to see if they represent numbers. This should include number representations with precision marks and scientific notation. NumberString ...
10
votes
2answers
532 views

Is there a way to identify a symbolic fraction?

Is there a way to use Head to detect a symbolic fraction? In particular I find, Head[a/b] Head[1/5] Times Rational ...
4
votes
4answers
187 views

Cases with Alternatives failed

Consider this list of rules rules = {a -> 1, b -> 2, c -> 3} I'd like to fish some of the rules out of such a list using ...
7
votes
5answers
327 views

Counting subsequences (i.e., patterns) within a list?

I would like to count the number of subsequences in list. Say I have data given by: data = {1, 1, 1, 2, 1, 2, 2, 2, 1, 2, 1}; I would like to count the number ...
3
votes
4answers
118 views
2
votes
3answers
106 views

Testing for a vector of reals [closed]

Suppose I define: RealVector[expr_]:=VectorQ[expr,NumberQ[#]&&Head[#]===Real)]; Then: ...
1
vote
1answer
71 views

How to use a list of rules as a data set

I have a file of models that I have saved that I want to be able to call in another program to be solved with NDSolve. Can I use ...
0
votes
1answer
162 views

Replacement of terms/Pattern matching involving products of derivatives of a function

In delving into Ramanujan summation, I'm trying to get a hold of the relations of the form $$\sum_{n=0}^\infty f(n)=\dfrac{h\frac{d}{dx}}{{\mathrm{e}^{h\frac{d}{dx}}}-1}\int_{0}^\infty f(x)\,{\mathrm{...
14
votes
1answer
140 views

Unexpected pattern matching behaviour: PatternSequence vs. Optional

fixed in 10.1 (windows) Consider the following pattern-matching expressions: ...
10
votes
5answers
307 views