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

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10
votes
3answers
438 views

substitution rules excluding subscripted variables

Suppose I have an expression containing p,Subscript[p,1],Subscript[p,2],etc. I want to ...
5
votes
1answer
165 views

How can I substitute something using only map?

For example, I have the equation x^2 + y^2 == x*y and I want to apply the rule y -> s*x I can do it easily by ...
11
votes
2answers
1k views

Simple problem with Manipulate and Plot

Would anyone have an idea why the following doesn't work: rule = {z -> x^2 + 2 x + y}; Manipulate[ Plot[z /. rule, {x, 0, 10}], {{y, 2, "y"}, 1, 5} ] But ...
2
votes
2answers
490 views

Mass Symbolic Manipulation with Subscripts? (from plaintext Input)

The simplest example of the change being sought is a greek letter, typed in as plaintext nu, and its may be replaced by the symbol, ν: expr = 3nu*kx*ky+ ...
12
votes
4answers
448 views

“Strange” behavior of Rule

According to the Help lhs->rhs evaluates rhs immediately. How to understand the output of the following code? ClearAll@x; {1, 3.5} /. x_?IntegerQ -> {x} ...
0
votes
2answers
92 views

Replace expression using a tuple

Given an expression in x, y, z (for example), and a list with three elements, like ...
0
votes
0answers
58 views

Problem using replace to simplify logarithms [duplicate]

Is there a way to combine logarithm terms like 9 m Log[m]-9 m Log[M]+16 m M Log[m]-16 m M Log[M] into ...
3
votes
1answer
442 views

Replace elements in a list

Suppose that I have a list: ...
1
vote
1answer
317 views

Arbitrary depth patterns/rules

Temporary message: I am now really confused. I am not sure how using Power and Unevaluated together works in the examples below. While answering this question, I stumbled upon the following. We ...
0
votes
2answers
367 views

characteristic polynomial based on differential equation

I have this differential equation: $$\ddot{x}-\frac{1}{6} \dot{x} - \frac{1}{6}x = e^t$$ When I DSolve it looks like this: ...
5
votes
2answers
140 views

Trouble with Replacements [duplicate]

I have the following line of code: Plus @@ Table[p[x], {x, 0, 20}] /. p[x_] -> Boole[MemberQ[{0, 5}, x]] The first part of this produces ...
1
vote
1answer
104 views

given n lists, get list of applications of function to n-tuples

Is there a built in function or an easy rule to do the following transformation? H[{A[0], A[1], ...},{B[0], B[1], ...},...] into ...
1
vote
3answers
182 views

Help me to find a way to do this repetitive stuff

I'm trying to do this: ...
18
votes
1answer
323 views

Why is ReplaceAll behaving like this?

I'm learning to use the ReplaceAll function and I found the behavior of which is quite confusing. For Sqrt[f[x, y]] /. f[___] -> u Mathematica returns ...
1
vote
1answer
228 views

Match and replace subexpression

I would like to replace the expresion $(n1-1)$ to $z1$ in following: In[1] := 2*n1*p[n1-1,n2] Out[1] := 2*(z1+1)*p[z1,n2] I have tried ...
8
votes
2answers
305 views

Unexpected behavior of rule matching a pattern

I am a beginner exploring the world of Mathematica. I expected the following code T[6, 5, 4, 1, 2, 3] /. {T[a___, 1, b___] -> Length[List[b]]} should return ...
11
votes
3answers
481 views

Replace operators

/. can be used to replace variables but how can one replace operators. For example in a * b, ...
3
votes
2answers
665 views
4
votes
2answers
98 views

Creating functions from output of other calculations

Apologies in advance if the title is vague, I'm not really sure what to call this. I have a function (call it 'foo') that generates a largeish polynomial, and it is natural to make the variables be ...
8
votes
3answers
264 views

Applying a transformation rule on an Image

I haven't been able to figure out why the following doesn't work: ...
2
votes
1answer
130 views

Replace an expression with a slightly tricky LHS transformation

I would like to make the substitution x^(11*y) -> r in the following equation x^(11 *y^z) - 1 to end up with: ...
5
votes
1answer
388 views

Why does this pattern for combining two lists require triple underscores (___) to work?

I understand that __ is a list of one or more elements, and that ___ is 0 or more elements, but when I try this rule with 2 ...
5
votes
1answer
213 views

Generating replacement rules programatically

I would like to generate sets of replacement rules programatically for predefining some permutations. So a function ...
8
votes
6answers
2k views

How to simplify a complicated Sum in terms of power Sums?

For example, I have: $a=\sum _{r=1}^n x_r \left(\left(\sum _{i=1}^n x_i-x_r\right){}^2-\sum _{i=1}^n x_i^2\right)$ ...
2
votes
1answer
69 views

Unique[] in RHS of rule

I have a function, explicit that takes dot product of two symbols, and replaces it with repeated dummy indices generated by ...
2
votes
2answers
122 views

Using a predicate to control the application of a rule in a replacement

How can I make a replacement rule that will only be applied to those parts of an expression that will not break a condition placed on the whole expression? For example, suppose I have ...
1
vote
0answers
44 views

plot[] with subsititution rule [duplicate]

I encounter this problem in Mathematica 9.0.1, I'm not sure if it ever happens in other version. Plot[{x, x + 1}, {x, 0, 10}, PlotStyle -> {Red, Green}] This ...
1
vote
3answers
154 views

Auto simplifications of power products

Mathematica automatically simplifies Exp[a]Exp[b] to Exp[a+b]. The problem is now that I can't do this ...
2
votes
1answer
151 views

How to transform an expression using algebraical instead of pattern rules [duplicate]

I would like to transform rules algebraically. A very simple example would be: - k^2 - 2 k x + x^2 /. {2*k -> 1} This transforms to: - $$k^2-2 k x+x^2$$ ...
8
votes
2answers
210 views

How do I write a function that can be used in a rule to modify both sides of an equation? [duplicate]

I sometimes need fine grain control over equations in Mathematica in order to help me understand how to solve a problem manually. A greatly simplified example of a session might be something like ...
1
vote
1answer
190 views

Efficient way to give symbolic elements symmetry

I have a symbolic expression that represents a set of operators. These operators have quite a bit of symmetry to simplify expressions: ...
7
votes
3answers
540 views

Piping and Replacement

I haven't been able to figure out how to use piping with certain functions. Specifically, I would like to apply a replacement at the end of a pipe, like the following: ...
0
votes
2answers
546 views

Converting a list of replacement rules into a list of real values [duplicate]

The following command outputs a list of replacement rules. ...
0
votes
1answer
146 views

How to change variable that has been defined in PDE?

I have a PDE function that contains a variable (named ka). I want to plot the result of my PDE in 1 plot using several different ka values. However, I'm not sure about how to write down this equation. ...
2
votes
2answers
525 views

Replacing values of a function

I have recently starting using Mathematica and have recently come to what seems as an impasse in my understanding of the language. If this is too "tell me how to do it" I would certainly understand. ...
4
votes
1answer
122 views

Replacing a combination of terms

I have a quite simple question. I have an expression that looks similar to $T=\frac{1}{a_1}-\frac{1}{a_2}+1$ and I'd like Mathematica to use $A=\frac{a_1}{a_2}$ to reformat the expression (if ...
3
votes
2answers
189 views

Efficient way of setting up a rule

I tried to define a simple rule defining how λ acts on ψ[n]: myrule1 = λ ψ[n_] -> α[n + 1] ψ[n + 1]; The result I get is ...
0
votes
1answer
378 views

Make Mathematica wait before replacing?

How can I force Mathematica to completely evaluate a subexpression before using a replacement rule? For example, consider the following definition (for the series of ...
0
votes
1answer
177 views

simplification rule with symmetry

What rule can you think of to replace the first line by the second? I have a bunch of expression like these, which I would like to simplify. All dependent cross terms must be written in the same ...
2
votes
1answer
227 views

A Sierpinski-ish structure, via 2D automata

The project is originally based on a puzzle proposed by EIORU at http://www.ptt.cc/bbs/puzzle/M.1342451949.A.00F.html (若您懂得讀中文 / if anyone happen to read Chinese^^) last July. The descriptions, ...
0
votes
1answer
168 views

Apply rule only if applicable? Check rule applicability? Custom unapplicable rule?

How to avoid recursion in the following example? ...
0
votes
0answers
42 views

How do I replace a variable with the answer from a solve function in the form k-> number + variables? [duplicate]

Possible Duplicate: Using the result of Solve in subsequent calculations extract values from replacement list I am trying to define a variable (k1) as ...
2
votes
1answer
114 views

Confused behavior using Dispatch to sort one list relative to another

I have a need to sort the entries of one list into the same sequence as the entries in a reference list. Because I have rather large lists involving strings, I'm trying to use Dispatch to accomplish ...
26
votes
1answer
1k views

replacement rules from a pattern and a matching expression

(This seems to be a very basic necessity in a language having pattern-matching capabilities such as Mathematica, yet I struggled for many hours to find a common solution to this problem.) Suppose ...
2
votes
2answers
239 views

Modify a sub-part of a sub-list only

I have this list: a = {{{0, 0}, {1, 7}, {2, 0}, {3, 2}, {4, 7}}, {{0, 0}, {1, 0}, {2, 1}, {3, 2}, {4, 7}}} and I'd like to transform it to this: ...
9
votes
1answer
349 views

error when defining a compiled function with ReplacePart

I always have difficulty in writing a non-trivial compiled function. I'm using Mathematica 9. Please see the following code ...
8
votes
1answer
242 views

Transformation rule on a list of non-negative integers

I am trying to create a transformation rule that takes a list of non-negative integer values of any length, finds a non-zero entry in the list, adds 1 to all preceding numbers, subtracts 1 from the ...
0
votes
2answers
276 views

How to use Solve rules as a function body?

Solve gives me an expression which I want to use as the body of a function. Rather than run Solve every time inside my function ...
10
votes
2answers
300 views

How to extract a specific element from EXIF photographic metadata?

It's now possible to import photographs into Mathematica and import the EXIF data at the same time: i = Import["ExampleData/coneflower.jpg", "ImageWithExif"] ...
8
votes
2answers
272 views

Replacing product expressions - named vs. unnamed pattern?

Suppose I have an expression of the form a b c d + x y z The FullForm of this is ...