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

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2
votes
2answers
174 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 ...
2
votes
1answer
66 views

What's the pattern that will match a head anywhere in an expression

I'm looking for the pattern patt[head] that will match any expression expr in which head occurs as a head anywhere within expr. ...
2
votes
3answers
550 views

Isolating a prefactor in an analytical expression

I have a large mathematica expression that looks roughly like f = A1 Exp[a1 x] + A2 Exp[a2 x] + b1/x + b2/x^2 + c0 + c1 x + c2 x^2 where all the $A_n,a_n,b_n,...
2
votes
2answers
60 views

Remove an element of a list [duplicate]

I want to check if any element of a list contains Missing["NotAvailable"] If so I want to delete the entire list. If I am correct I need to have some ...
2
votes
1answer
35 views

Evaluation of BlankNullSequence inside StringReplace

I would like to replace the occurrence of "a(x)" and "b(x)" in a list with "a(x-na)" and <...
2
votes
1answer
45 views

Default value behaves differently when used in Function and when used with Cases

Consider this example: Cases[{4, x, 5 a , 6 x}, x_.*a_ :> x] (*{1, 1, 5, 6}*) It is clear that the _. took 1 as a ...
2
votes
3answers
377 views

Mathematica won't plot the a function that is solved from NDSolve

I have used NDSolve to solve for a function (an angle of a triple pendulum), and now I wish to plot the derivative of that function (the angular velocity). ...
2
votes
1answer
296 views

Deleting empty cells and selecting cells matching a pattern

Is there any way for me to automatically select all cells that are completely empty? You know, those cells that you create but end up cutting what's in them and paste it somewhere else, so after a ...
2
votes
2answers
283 views
2
votes
1answer
76 views

How can I get the functionality of a command ReplaceAllList?

I'm trying to use ReplaceList to match subexpressions. I expected the command: ReplaceList[{p, {p, p}}, {x_, y_} -> x y] to output two results, equivalent to: ...
2
votes
1answer
127 views

Function to differentiate between date pattern and specific string format

I'd like to write a function that behaves one way when the argument is a Mathematica date, such as {2013,12,15}, or with added hours, minutes and seconds if ...
2
votes
1answer
282 views

Using transformation rules to manipulate expressions

I'm trying out Mathematica as a replacement for LaTeX for typesetting math. It works very well, but I would like to take advantage of Mathematica's computer algebra capabilities as well. Specifically, ...
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.: <...
2
votes
1answer
136 views

How to use slots and patterns to reduce repetitive calculation?

This is kind of complicated... How can we make MMa calculate values of a function before doing multiple pattern or slot substitutions? Answers to similar questions didn't cover the case where the ...
2
votes
1answer
45 views

Linear function on strings using UpValues

I have two functions Sup and Sdown that take a string of letters with allowed characters ...
2
votes
1answer
229 views

Functions that operate on symbolic matrices?

I'd like to write functions that operate on symbolic matrices, and do nothing when fed anything else. ...
2
votes
0answers
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 <...
2
votes
0answers
59 views

Pattern Matching and overloading NonCommutativeMultiply [duplicate]

My goal right now is to implement some rules like linearity etc for noncommuting operators (arbitrary matrices etc). This is partly an exercise for me to understand MMA better so giving me a package ...
2
votes
0answers
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 ...
2
votes
0answers
59 views

How do I let Fourier Transform know that it is a linear operator? [duplicate]

I have the following issue with FourierTransform, Fourier transform doesn't seem to know it is a linear operator. ...
2
votes
0answers
58 views

pattern matching and applying a function, not working as expected [duplicate]

Consider the following code G[x, y] /. a_[b__] -> Total[a @@@ Permutations[List[b]]] I expect it to give G[x, y]+G[y,x] ...
2
votes
0answers
100 views

Understanding the order of applying Rule to expression [closed]

I am a little confused about: In what order is a Rule tried to apply to an expression? In a depth-first order or otherwise? For example, ...
2
votes
0answers
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 ...
2
votes
0answers
37 views

Detecting a more general pattern [duplicate]

I need a function that, given 2 patterns, determines if the first pattern is more general than the second (i.e. that any expression successfully matched by the second, will be successfully matched by ...
2
votes
1answer
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 ...
1
vote
3answers
2k views

How do I combine the data from two tables according to a rule of my own devising?

I have two matrices a = m x 5 and b =m x 5 (m is large, say 1,000) which are already sorted as below: How to generate a new matrix c = m x 5 which consists: Column 1: exact replica of Column 1 ...
1
vote
3answers
248 views

Command like “find” in Matlab [closed]

Is there a command working exactly like Matlab's find? I know that Pick might work, but I just want to give a logic condition ...
1
vote
1answer
788 views

What does the slash-colon symbol do?

I came across a bit of code that uses the syntax /: and I don't know what it does. I can't find its documentation, or maybe I'm just not looking properly. The code ...
1
vote
1answer
80 views

Can I map a function over a sequence of arguments without making the arguments into a list first?

I would like to set evenFunction[f_][a_, b_, c_, ...] = f[Abs[a], Abs[b], Abs[c], ...] I have come up with two ways to do this so far. Use pure functions <...
1
vote
3answers
158 views

Making a replacement on the numerator and denominator of a rational number

It's isn't a big deal, but when I run the following I don't get the output I expect. After discussing this in the comments it appears it has to do with being an atomic expression. ...
1
vote
2answers
171 views

Named patterns as function argument descriptors

I have a function timeToMinutes that takes a 24-hour time as a string argument (in digital clock format, e.g., "15:47") and converts it to the number of minutes ...
1
vote
2answers
177 views

Using patterns in ReplaceAll to extract elements from tuples at arbitrary depths

Please consider the following: I need to extract from MyList all last parts of each 3-tuple. ...
1
vote
2answers
76 views

Patterns with inactive integrals

I am trying to do algebra on unsolved integrals but not getting the pattern-matching right. I want the correlation of f[x] and f[x]+a*d[x], normalized by their self correlations. ...
1
vote
2answers
121 views

text analysis: split document in seperated lines

For a text analysis I want to split a large document in seperated lines. Then I want to calculated for example the average number of words. A example of the document is the following: ...
1
vote
4answers
186 views

Need an efficient way to do this list manipulation

Lets say i have two lists with me as given below: l1 = {4, 6, 8, 9, 10, 12}; l2 = {2, 3, 4, 5, 6, 7}; Now i have a function S2P(details irrelevant) which takes ...
1
vote
2answers
349 views

How to generate patterns by a list of integers

I have a list of integers {3,4,2,2}. This list will give patterns {x_,_,y_,y_,_,_,z_,z_,w_,w_,x_} and ...
1
vote
2answers
111 views

Filtering and summing sublists with Cases

I've declared a list: list = {{1, 2}, {2}, {3, 4, 1}, {5, 4}, {3, 3}, {a, b, c}, {e, f}, {g}, {}, {Sin[a], Cos[b]}}; now I've made an rule which add 2 pairs ...
1
vote
2answers
77 views

What is the role of the pattern object in this implementation?

In the documentation I found a nice idiom which allows me to do model fitting with interpolating functions. I think this kind of thing is amazing and a credit to the utility of an environment like ...
1
vote
1answer
36 views

ReplaceAll - Position of list arguments not displayed properly [closed]

This code A[1, 2, 4, 5] /. A[a___] -> Position[{a}, 4] return {} Why this code not return 3 (a position of number 4) ? I ...
1
vote
2answers
40 views

“Nonatomic expression” error when identifying certain positions in a list [duplicate]

Please can anyone help ? I have a list of sets, and I am trying to find the positions in that list of those sets which are subsets of a given set. (Here I am ignoring the distinction between lists and ...
1
vote
2answers
94 views

Removing solutions which are particular cases of others

I have an algorithm which gives me a list of solutions (in matrix form, if it is of any importance) of an equation. Some of these solutions are particular cases of other. For example, in this list ...
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
97 views

Function returned an unexpected list

I was trying out a question in Wellin's Programming with Mathematica that says the following. Question: Given a set of points in the plane (or 3-space), find the maximum distance between any pair of ...
1
vote
1answer
821 views

How to effectively compare two sentences and say both are equal

want to compare two text file. Suppose file AA contains following text ...
1
vote
1answer
43 views

Pattern matching for product of two terms fails if one factor is 1

I have a long set of replacement rules that I utilize to solve some longish integrals over trigonometric functions. Just look at this snippet (from this answer): ...
1
vote
1answer
104 views

How to write or extend operators like $*\!\!*$

I'm stuck on trying to define simplification rules for NonCommutativeMultiply, much like ExpandNCM found in Documentation Center, under Applications. For example, I'd like ...
1
vote
2answers
64 views

Substituting a list of values into a function [closed]

g[p_] := Mod[19^(-1 + p), p^2] This is my function, and the set of values I have is the first 999 prime numbers. I made a table listing the first 999 prime ...
1
vote
1answer
60 views

How to use EvenQ[] in patterns? [duplicate]

This works: (w[1] + w[2] + w[3]) /. w[s_] -> If[s == 2, w[s], 0] (* w[2] *) This doesn't: ...
1
vote
2answers
108 views

Get the sum with cases

I have the following list: list = {{1, 2}, {2}, {3, 4, 1}, {5, 4}, {3, 3}, {a, b, c}, {e, f}, {g}, {}, {Sin[a], Cos[b]}}; I should use ...
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 ...