Questions about Mathematica's rule-based replacement functionality, including functions such as Rule (->), Replace, ReplaceAll (/.) and ReplaceRepeated (//.).

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1answer
75 views

Apply solution rules to new functions as parameters [duplicate]

Update: I put an screenshot of how my code and problem look like at the end. Say that Mathematica solved a system of equations and got two answers {{a -> 3, b -> c, d -> 0}, {a -> -3, b -> 0, c -> ...
0
votes
4answers
57 views

How to trim out sequence of blank-spaces?

Considering we have few strings: s1 = "dasbdk " s2 = "asdnkal asn knkl nkn dvklsn " s3 = " jbjkbasd nklnkln " Q1: How can the blank-spaces in ...
0
votes
0answers
87 views

Replacing function in Sum

I have this expression, which, after execution, gives these $F[s,r]$ in output. $$ S_{1,1}=\sum _{s=1}^{16} \sum _{r=1}^{16} F(s,r) \text{Tr}\left[G_r.G_1.G_s.G_1\right] $$ Here is a piece of ...
2
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3answers
115 views

How to check keys and values in nested Associations?

Considering we have a an association: ...
1
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1answer
58 views

Concatenated rule applications (applying rules to rules correctly)

I am trying to apply a series of individual rules onto an expression sequentially, but also not have to write out the repeated ReplaceAll functions each time I want ...
0
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1answer
68 views

Replacing every nth comma in string output with “\n” [closed]

Feels like a strange question to ask, but I basically have a string with sets within sets, and it seems like the simplest formatting solution to seeing the data without needing to import everything ...
2
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1answer
50 views

Conditional replacement syntax

Why does the following expression not do what I expect Array[a, 6, 0] /. a[__?MemberQ[{1, 2}, #] &] -> 0 I expect ...
2
votes
1answer
94 views

What's the difference between functions and replacement?

I used to thought that calling a function is equal to applying a rule, i.e. applying a rule of f[x_]->sth. is equal to calling a function f with definition f[x_]:=sth. However, given ...
0
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1answer
60 views

Setting a range of values to one value [closed]

My question is perhaps worded a little vaguely, but it's a problem I'm running into defining my own function. I'm drawing some shapes with variable height, and sometimes this height is 0. For it still ...
0
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1answer
71 views

Substituting inside a differential equation

x y''[x]+2y'[x]+l^2 x y[x]==0/.y[x]->Cos[x] I think above code shows what I want to do quite clearly. How do I make it happen. Only y[x] is replaced.
1
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1answer
108 views

A puzzling result of the `ReplaceAll` [duplicate]

I tried to do something below Log[PDF[NormalDistribution[m, s], x]] /. Log[u_[x__] ] :> Plus @@ Log[List[x]] which gives a desirable result that splits the ...
1
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1answer
59 views

Using HoldForm for a changing list

I have a 'list' of the form an expansion: F = (A[1] + A[2])(B[1] + B[2]), such that F[[1]] produces the result ...
1
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2answers
114 views

why does replacement rule not work

Why does the following replacement rule not work? term = x^2/y^2 + x^3/y^3 term /. u_^p_/v_^p_ -> z^p I expected it to return ...
3
votes
3answers
92 views

How to apply ReplaceAll to denominator?

Here is the simple task. In reality, it's far more complicated, but it comes down to this. I want to take the expression $\frac{y}{x^2}$ and replace $x^2$ with $k$. This doesn't work: ...
0
votes
0answers
51 views

Mathematical symbol and name for Symbolic Replacement

(Originally from math.SE, but might be better here) I'm searching for a mathematical symbol, that describes the symbolic replacement done for instance in Mathematica: ...
1
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1answer
140 views

Making ReplaceAll faster

I have a list of functions ncalc that is calculated by ...
2
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1answer
52 views

Pattern matching & simple replacement

I have a question about an expression that I want to modify. Here is the expression: ...
8
votes
1answer
242 views

Why is `Block` significantly faster than `ReplaceAll` for inputting variable values

Given that the documentation for FindMinimum uses ReplaceAll for its various examples of what to do with the found solution to ...
10
votes
1answer
272 views

Is there a programmatic equivalent of Edit > Find…?

Most things that can be done via the front-end interface in Mathematica can also be accomplished by some function. Is that the case for find-and-replacing? That is, is there some code I could execute ...
0
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1answer
91 views

Applying ReplaceAll to I (imaginary unit) [closed]

Why does I/.I->-I return -I but Exp[-I]/.I->-I yields ...
1
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1answer
142 views

Why does it matter at what point I replace?

I need to find four orthogonal linear combinations of complicated functions, that vanish at four different points. I use (LK4 is defined below, but its shape should have nothing to do with my ...
1
vote
1answer
83 views

Why does ReplaceAll behave so oddly?

ReplaceAll can behave a bit oddly. Consider ...
1
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1answer
45 views

What particular situation do we have to use RuleDelayed after replacement? [closed]

On the answer of How to impose normalization condition (not initial condition) on DSolve or NDSolve? k = vars /. sol /. cs[[1]] /. C[_] :> 0 // N; I see that ...
2
votes
1answer
54 views

Mathematica does not replace \[ImaginaryI] inside Hold

Mathematica 10.1 does not replace I (i.e. \[ImaginaryI], the square root of -1) inside functions with the Hold attribute. Example: ...
0
votes
1answer
101 views

Replace instanced variables within module-return functions for dynamic Tooltip

Currently I am stuck with the issue of renaming an instanced variable like r1$38655 to a global one. The function is created within a "localizeAll" Module. Here's ...
1
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1answer
76 views

Replace symbols in output without evaluation

I found the Wolfram example for ExpandNCM but I want a more human-readable output form. I want to evaluate ExpandNCM, for example with ...
0
votes
0answers
70 views

Matrix iteration failing after second step

I am calculating 11x6 matrix using different logics as in below code. Problem is in Do loop in below code where I have two different criteria to update matrix "fd". I am expecting logic in IF which ...
0
votes
1answer
57 views

Replace element of matrix based on rule which invloves other element of same matrix

I am trying to replace 1s row of matrix d iteratively from right by multiplying last element in 1st row with (1-int*dt) to generate 2nd last element. The replacement continues till I reach the 1st ...
0
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0answers
26 views

Convert the output of solve into equality [duplicate]

I know this is has been asked before but seriously, none of the ones I checked helped because they referred to a single variable assignation. Apologies if this is a duplicate. I have many variables ...
0
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1answer
57 views

Why won't the Rule work? And how to apply it to a combination of variables?

I want to convert SI to Gaussian units given vectors: ...
0
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2answers
51 views

How can I match some parts of an expression?

Suppose I have an expression like Abs[x+I y]+Sin[Abs [c+ I (d+e)]], and I want to replace all expressions in the form of ...
1
vote
3answers
147 views

How to do a Check for every element in the list?

I know how to do a Check for the list in general: ...
0
votes
2answers
50 views

Different behaviour of Map and Inner in replace rules

Why does x[{1, 2}] /. {x[l_] -> Map[func, l]} {1, 2} not behave as expected, while for example ...
2
votes
4answers
255 views

How to switch from array to string?

Considering we have an array: a = {2/3, 4/5, 9/7, 3/7, 1/7, 1/9}; How can I get this to be: "2/3 4/5 9/7 3/7 1/7 1/9" ...
6
votes
5answers
403 views

How to switch from List of rules to Association? [duplicate]

Considering we have a list of rules: ...
6
votes
4answers
352 views

How to delete Missing[“NotAvailable”] from list of rules? [duplicate]

Considering we have a list of rules: ...
1
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2answers
125 views

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

Why is "Xabcde" /. "X" ~~ e__ -> e "Xabcde" and not "abcde"
2
votes
3answers
145 views

How to delete a pattern from String?

Having a string like : "{Aaaa -> a, Bbbb- > b, Cccc -> , Ddddd -> c, Eeeee -> , Fffff -> e}" I want to delete the parts that contain ...
0
votes
1answer
48 views

How to manipulate string parts?

Let's consider I have following string: "{a-> POR, b-> D610, c-> 0, d-> \"300/7\", e -> \"1/400\"}" How can I run over and update anything that is ...
3
votes
1answer
105 views

How can I solve my easy system of equations?

I am new to Mathematica and am afraid this is a silly question. I have this very easy substitution, it has three equations on three unknowns {w1, l1, t1}. I want to ...
0
votes
3answers
90 views

How to iterate through a list of rules?

Let's consider I have a list of rules: {Aa -> 1/2, Av -> 2/5, Bx -> 3/7, Ce -> 4/9, ...} I want to find all keys that contain the letter "A" and ...
1
vote
1answer
66 views

Replace Coefficients of multivariate expressions by numbered constants

I have an expression which is a polynomial in Delta, xi and phi. The prefactors are huge ...
0
votes
1answer
25 views

How to apply substitution when expression contains powers of the quanity

An expression like: a = TrigToExp[ 3 + 4 Cos[u] + Cos[ 2 u]] produces a list of exponential factors: 3 + 2 E^(-I u) + 2 E^(I u) + 1/2 E^(-2 I u) + 1/2 E^(2 ...
1
vote
1answer
105 views

Applying functions repeatedly on parts of complicated expressions

I am dealing with expressions like $$ \textrm{expr}=5D_{4,1}\langle12\rangle\langle23\rangle\big(-\langle15\rangle^2\langle24\rangle\langle34\rangle + ...
7
votes
4answers
463 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
2answers
77 views

Problem with Replace function [closed]

I recently started using Mathematica. I'm not able to understand my mistake. I'm trying to implement the Frangi vesselness for the enanchement of vessels in biomedical images. I wrote these functions: ...
1
vote
0answers
54 views

Substitution does not work while substituting with a value from list [closed]

I am writing a program which iteratively solve and make substitution from a list. As I have shown in the code substitution works when I enter the value directly (Input 100). When I extract the same ...
0
votes
2answers
61 views

For the same function, why does /. give a complex result?

I define a very simple function like this, g[k_] := 1. + 2 Sum[1/(1 + (2 n)^2), {n, 1, k}] g[50] give the result is: 1.70279. But g[n] /. n -> 50 give aother result: ...
3
votes
2answers
186 views

How to rewrite the rules in a list when they satisfy a given condition

I think the best way to state my problem is to illustrate it with an example. Assume I have the following toy-list of rules: ...
4
votes
3answers
206 views

Replace elements in matrix to make it symmetric using automated procedure

I am generating a matrix using (mat2 = Array[Subscript[a, ##] &, {4, 4}]) // MatrixForm but would like to force Mathematica to make it symmetric. Thereby I ...