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

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6
votes
1answer
286 views

ReplaceAll inside an Iterator

I'd like to apply a set of rules to an expression defining the iterators of the table, like this: ...
3
votes
3answers
554 views

How to replace all occurrences of an element in a list?

Consider the following: list={1,2,2,2,3}; I would like to replace all 2 with the string "Test". ...
13
votes
6answers
2k views

Replacing composite variables by a single variable

To replace a single variable by another variable, one can simply use the the replace all (/.) operator (e.g., ...
19
votes
2answers
1k views

Extracting values from nested rules in JSON data

I have been using Mathematica to analyse some data from the StackExchange API. It is conveniently available in JSON form, which Mathematica interprets as replacement rules. However, some of the rules ...
9
votes
3answers
513 views

How to implement a regular grammar?

What is the most simple, elegant way of implementing a rewrite-system defined as: $$ \begin{aligned} \Sigma &= \{a_1, a_2, a_3, ...\} \\ N &= \{A_1, A_2, A_3, ...\} \\ \{\alpha_1 , ...
8
votes
2answers
612 views

Mathematica rule substitution memory

First I present the specific programming question, and then I provide further background details. Given an expression in Mathematica, say f=3x+7y, there are two ...
3
votes
3answers
688 views

Changing variables algebraically

Suppose one has two functions, $y(x)$ and $z(x)$, and one seeks to obtain $y(z)$ by substituting $x(z)$ into $y(x)$. Can this be done in a single step? Or must $z(x)$ first be inverted independently? ...
6
votes
3answers
574 views

Arithmetic operation on the value returned by Solve

I want to modify the value that is returned by Solve. Example: SolC1 = Solve[Sin[ π x / L] == 1, x] {{x -> L/2}} I need to add n to x so that x becomes ...
15
votes
3answers
568 views

Using results of Reduce

Suppose I have function f: f[x_, y_] := 50000 + x 30000 + y 35000; Now I want to find the x and y when f[]<=200000. I use Reduce: ...
6
votes
3answers
290 views

Replacement rule only matches part of expression

I have the result of a calculation (which is too long to mention here) and it gives ...
4
votes
1answer
153 views

Replace rule does not match

I have the following expression -3 I Ez Re[Ex] + 3 I Ex Re[Ez] And I wish to write this in the form ...
4
votes
1answer
255 views

Replace rule also matching complex numbers

I'm having the replace rule: rule = {-g_ x_^4 - 2 g_ x_^2 y_^2 - g_ y_^4 -> -g (x^2 + y^2)^2}; Now, ...
9
votes
3answers
804 views

Replace expressions with symbols

First of all: I'm new to mathematica, so I would appreciate it if the answers are quite complete. I have the result of calculation that is expressed in $\sin$ and $\cos$. Now, all of these can be ...
10
votes
7answers
2k views

How do I replace a variable in a polynomial?

How do I substitue z^2->x in the following polynomial z^4+z^2+4? z^4+z^2+4 /. z^2->x ...
32
votes
3answers
445 views

Replace inside Held expression

I wish to make functional replacement inside Held expression like this: ...