Questions tagged [replacement]
Questions about Mathematica's rule-based replacement functionality, including functions such as Rule (->), Replace, ReplaceAll (/.) and ReplaceRepeated (//.).
1,081
questions
0
votes
0answers
30 views
How to replace a function [duplicate]
I want to replace the function y[x] in the following expression with function y[x]=x^2
...
0
votes
0answers
27 views
replacing a founded value in a function
Here is the sample
F[r_] := r^2 + r^3
DerivI[r_] := D[F[r], r]
A = FindRoot[DerivI[r], {r, 9}]
B = F[r] /. r -> A
I want to replace ...
1
vote
0answers
22 views
Simplify each coefficient of coefficientlist individually and automatically substitute any repeats
I have a 13x13 polynomial coefficient list that I create with:
CoefficientList[Expand[myequation] /. Equal -> Subtract,{x,z}]
I would now like to simplify ...
1
vote
1answer
40 views
How to deal with procedurally generated rules and patterns?
I'm trying to procedurally generate replacement rules of the following form
...
0
votes
0answers
58 views
Teach Mathematica analytical continuation of the gamma function
If I ask Mathematica to compute the gamma function for me
Integrate[Exp[-s] s^(a - 1), {s, 0, Infinity}]
It dutifully returns to me
...
1
vote
2answers
44 views
How to apply different rules to multiple appreances of the same variable?
For example, I have two lists. The first list listA = {x, x^2, x^3} has some elements involving the same variable x. The second ...
0
votes
1answer
52 views
Converting numbers and expressions
Trying to create a rule to convert negative numbers/expressions positive.
So far:
f[-x_]:> f[x]
Trying to extend this rule to floats such as -1.0 and ...
2
votes
4answers
131 views
How to replace the string
How to replace the string k with 1*^3 and Hz with blank space, such that I could use ListLogLog[]
...
4
votes
1answer
56 views
Replace pattern with the number of matches so far
I want to replace a n-th pattern match in an expression with n. This is a very simple task, though it appears very hard to find an elegant implementation.
For example, with input
...
1
vote
2answers
55 views
Assigning values to multiple variables from a list
I have a solution of the following form:
$F(x)= \\
\qquad c+(x_0+x_1+x_2+\ldots +x_n)- \\
\qquad (x_0\,\log(x_0+\sqrt{x_0})+x_1\,\log(x_1+\sqrt{x_1})+x_2\,\log(x_2+\sqrt{x_2})+\ldots +x_n\,\log(x_n+\...
0
votes
1answer
31 views
Making substitution to an expressions with a list of numerical data [closed]
Suppose I have an expression similar to this: y=23.23*(h[x]^2)*(D[h[x],x])*(D[h[x],{x,3}])/(13.2+Cos[0.245x]) The actual expression is a lot more complicated, but ...
4
votes
4answers
196 views
How can I use the solutions of coupled nonlinear equations as functions of its parameters?
I have a set of coupled nonlinear equations.
I want to plot all the possible solutions as functions of the parameter AA.
I have tried this code but it does not work.
...
8
votes
2answers
309 views
StringReplace with multiple patterns
I am experiencing what seems to be a strange behaviour with StringReplace while trying to add an extra pattern to an existing list of patterns.
The problem is to translate a string into Morse code, ...
1
vote
0answers
63 views
Find all pattern in expression
Consider this problem: I have a functional $\mathcal{F}$ acting on some function $n(t)$ such that
$$
\mathcal{F}[n(t)]=0
$$
$$
\mathcal{F}[n^*(s)n(t)]=\alpha(t,s)
$$
$$
\mathcal{F}[n(s)n(t)]=0
$$
...
3
votes
3answers
163 views
Trying to replace the text E with scientific notation
How to replace the E with scientific notation *^?
...
2
votes
1answer
54 views
Rewriting a plot expression to add an option works, but with an unexpected error message
I'm trying to rewrite a ListDensityPlot expression to systematiccaly add an option:
...
6
votes
3answers
114 views
Convert logical combinations from Reduce to a usable function
I'm working on a geometry problem and would like to create a function to create a triangle based on the logical constructs output by Reduce but cannot obtain all the constructs. Here's the problem:
...
3
votes
1answer
41 views
How to make function act on (multiple) replacement variables [closed]
I have a function which returns an algebraic expression corresponding to a "jump" between two ordinates, for example $[x]=x_2-x_1$. The function applies for any choice of variables and labels. The ...
4
votes
4answers
89 views
ReplaceList doesn't apply rules down to subparts
Somewhat related to a previous question, I'm experimenting with ReplaceList to get the list of all possible transformations we can obtain by applying a rule to an expression. But I don't manage to ...
1
vote
1answer
34 views
Annotating variables in replacement rules
How do you decorate or annotate a variable in a replacement rule?
For example
{(e[(-X + Y)^2 || f])} //. {e[(-a_ + b_)^2 || f] -> (-a + b)^2}
Would ideally ...
3
votes
1answer
65 views
ReplaceRepeated with special characters: Alternatives
Following the advice here, I tried to replace part of an expression guided by the FullForm details:
...
2
votes
0answers
51 views
General rule to rewrite function and argument into a new symbol
I am trying to convert Mathematica output into equations I can plug into C. I am presently trying to convert expressions of the form
Derivative[1,0,0][f][t,x,y]
...
3
votes
7answers
224 views
Obtaining the terms of a summation alongside the result
I have a Sum expression:
s := Sum[2x,{x,0,3}]
As an exercise to explore the rewriting capabilities of the Wolfram Language, I ...
2
votes
2answers
48 views
How to encode this rule (for visualization, etc) similar to cellular automata?
I came across this rule on Twitter and it reminded me of the cellular automota discussed in NKS:
How to encode this in Mathematica for (visual) inspection?
4
votes
2answers
72 views
Extracting values from function/list containing arguments/elements (using patterns)
Here's an example input list:
...
0
votes
1answer
56 views
A single expression that performs substitution and simplifies a trigonometric form [closed]
I'm very new to Mathematica. I searched through the online documentation, but I don't understand why it realizes that $\sin(n\pi)$ for $n\in \mathbb{Z}$ is $0$:
...
0
votes
1answer
44 views
How to turn a matrix into a 'function'? [duplicate]
I have some codes to turn a set of equations into a matrix. Suppose the matrix Lis expressed in terms of variables $\epsilon$, $K$, $M$, and I want to make a ...
0
votes
1answer
51 views
Problem with replacement rules
I would like to apply substitution rules to an object I have defined, but I must be doing something wrong. Here are the relevant pieces of code. First I have defined a function ...
0
votes
2answers
60 views
Simplifying polynomial in one variable by substitution
I want to simplify a polynomial in variable $x$ with integer coefficients by substitution $x\to{x}/d$ so that the coefficients become smallest possible integers.
Input:
...
2
votes
1answer
36 views
0
votes
0answers
44 views
Delayed Rule right-hand-side mis-evaluation
Outline
I am trying to create a rule that will give me a minus sign if the number of times A is applied on X is odd where A is some οperator and X a random quantity.
Some of the configurations of ...
1
vote
1answer
38 views
Filter out terms that include any combination of F[X] and G[-X]
I have the following problem which is closely linked to a previous question I asked some time ago (Replacement rule for terms that are separated by operators?).
In this specific instance, suppose I ...
0
votes
0answers
33 views
Rule Replacement Fails with Embedded Conditional
I was using a rule replacement that creates a matrix. At one rule, I added a conditional to return one vector and then added that (after the conditional and within the same replacement) to another. ...
1
vote
1answer
36 views
1
vote
0answers
36 views
The replacement function is an integral and the double integral yields a different answer than the normal double integral
I am fairly new to Mathematica. I have a quick inquiry. The code is simple and just 3 lines. Trying to do a replacement rule as follows
...
6
votes
1answer
90 views
ReplaceList Except Alternatives bug
Bug introduced in 11.3 or earlier and persisting through 12.0 or later
[CASE:4352435] and [CASE:4354378]
In Mathematica 11.3 and 12.0,
...
0
votes
2answers
71 views
Suppress arguments in output for pretty print
I would like to define a rule that suppress any arguments of a function for visibility.
I tried:
rule = f_[x__] -> f
While this works well with individual ...
2
votes
1answer
58 views
Handling a list of variable assignments to be used with `With` [duplicate]
Is there a way to use With as follows?
variables := {a = 2, b = 3};
With[variables, a^b]
Desired output
...
0
votes
0answers
36 views
making replacements when patterns don't match exactly
I want to simplified some mathematical expressions, and they are similar to
...
1
vote
1answer
47 views
TagSetDelayed for spotting zero derivatives
I am trying to implement my own differential operator, d[arg_, var_],
that computes the derivative of arg w.r.t. ...
0
votes
0answers
31 views
Tracing & Modifying a Function (Replace All) [duplicate]
For the function:
f[x_Plus] := Apply[Times, x]
f[a + b + c]
Out[]= abc
This is clear, as the Times is applied to the list with Plus head in f.
However, when ...
1
vote
2answers
37 views
Manipulation replacements rules from Solve [closed]
Assume the call to the routine Solve[eqn==0,{x1,x2}] returns:
{{x1->a1,x2->a2},{x1->b1,x2->b2}}
I would like to ...
0
votes
0answers
37 views
Replacing in FeynCalc
I started to take the trace of some terms in FeynCalc package. I encountered a problem in replacing. Here is my problem:
...
3
votes
3answers
67 views
Assign Values from Array to Array [duplicate]
I am trying to simply do the following
cVec = {a,b,c,d}
From another expression, I obtain another vector, say,
...
0
votes
0answers
26 views
Variable subscript substitution - easy way?
I have a Mathematica expression with about 900 terms, that looks roughly like this:
$X_{1,1} + Y_{1,2} + Z_{1,3} + XX_{1,4} + XY_{1,5} + ... $
Is it possible to perform a fast method to copy this ...
0
votes
0answers
39 views
Implementing a generic product rule
I'd like to implement a generic rule for expanding differential forms by the product rule. For instance, I'd like to transform the following PDE:
$\phi \frac{\partial \phi}{\partial t} = \phi \nabla^...
3
votes
1answer
36 views
Prevent argument substitution in held expression when injecting into unevaluated code
I want to write a custom sow/reap pair to wrap any piece of code in sow[code] and call reap ...
0
votes
0answers
54 views
Derivative operator w.r.t a vector index and change of variables
Description and code lines:
Define a scalar product to represent $A_i·A_j$ , $A_i ·B_j$ and $B_i ·B_j$, such that $A_i · A_i$ = 0.
This is implemented in the following way:
...
1
vote
0answers
38 views
ReplaceAll on a Plot - Can you reproduce this error?
The weird thing is that it occurs only the first time I evaluate it!
The same happens with Plot but not with Graphics.
I can ...
0
votes
1answer
24 views
Plot with substitution of domain values before evaluation of function
I have a function of two variables $f(x,y)$. I find the maximum value of $f(x_0,y)$ by first substituting the value of $x=x_0$ and then maximizing in the range $0<y<1$.
My question is: How to <...
