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

learn more… | top users | synonyms (4)

3
votes
1answer
152 views

Set promotes Rule to RuleDelayed?

In mentally building a model of how Mathematica works, I naively expected Set to create a Rule in a symbol's ...
9
votes
4answers
225 views

Leave expression tree formatting the same when a replacement rule is applied

If I type e1 := 3 x + 2 (1 + y) z // TreeForm, I get an expression tree. If I then type e1 /. x -> 3, I get another ...
4
votes
3answers
1k views

Replace function and its derivatives found with Solve

If I have an equation eq = f[x] + g[x] == 0 and I solve for f[x] sol = Solve[eq,f[x]] ...
0
votes
1answer
135 views

Numerical rule evaluation -> {True, False} to deviation of target equation

I solve some equations numerically with FindRoot[] returning a quadruple {1,2,3,4}. Because the solver sometimes do not find any roots depending on parameterization of these equations I select only ...
8
votes
2answers
198 views

Representing a value in an output as a self defined variable

I'm trying to find a way to have Mathematica always represent a numerical value as a self defined variable that I define using lhs=rhs. For example, if I execute ...
4
votes
2answers
696 views

Replace expressions by self defined symbols

I have a list of expressions like the following: ...
5
votes
2answers
750 views

Speeding up mathematica by subsitituting numerical values

According to this Wolfram Blog post, one can speed up Mathematica code by substituting numerical values as soon as possible. How does one substitute before the main expression is evaluated? The ...
6
votes
1answer
474 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: ...
4
votes
3answers
1k 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". ...
14
votes
6answers
3k 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., ...
21
votes
2answers
2k 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 ...
11
votes
3answers
892 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
734 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
1k 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
741 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
874 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
378 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
181 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
308 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
1k 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 ...
12
votes
7answers
3k 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 ...
40
votes
3answers
1k views

Replace inside Held expression

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