Questions tagged [replacement]
Questions about Mathematica's rule-based replacement functionality, including functions such as Rule (->), Replace, ReplaceAll (/.) and ReplaceRepeated (//.).
1
vote
1answer
33 views
Replacing with Elements from a List [duplicate]
I have a fairly complicated expression with nested lists and I want to substitute a given string for each integer. Here's a simple example where ind is my integer-valued data structure and names is ...
1
vote
0answers
21 views
Moving to the last placeholder with inputautoreplacements
I have had a long-standing problem when I try to use my inputautoreplacements in a text cell. The replacements I have made include boxes that include placeholders.
When in the text cell, you type ...
4
votes
1answer
90 views
A single argument pattern definition applies to multiple-argument patterns?
Consider defining a pattern rule, such as
myFun[x_]:=x
As far as I understand Mathematica syntax, this rule means
...
1
vote
3answers
91 views
Substitution in expressions
As the title suggests, I want in an expression to to some substitutions. For example in the expression $\mathcal{L}^+_0+\mathcal{L}^-_0+\mathcal{L}^+_0+\mathcal{L}^-_0+\mathcal{L}_1$ I want to ...
0
votes
1answer
45 views
Replacing a derivative [closed]
If I want to calculate e.g. $\frac{dr(t)}{dt}$ then in Mathematica we can write e.g. ,
answer = D[r[t],t]
This outputs r'[t] ...
0
votes
1answer
37 views
constructing Matrix from coefficients of solution & assigning 0 for empty Cells [on hold]
i tried to construct a matrix from the coefficients of my solution, but problem that;
1; how can i get coefficients out of Solve
2; some Matrix elements are empty so i must assign 0 in those empty ...
0
votes
1answer
46 views
Replace constant in summation function using replace or If or /
Hi i how do i replace constant for k in this summation.
For following:
Even 2*n Even replace k by a
Even 2*n+1 Odd replace k by b
Here is the code
...
5
votes
1answer
46 views
Inconsistent application of replacement rule
I want to use a replacement rule to change log[var] into var inside a function. A minimal example follows. In one case it ...
4
votes
2answers
91 views
Finitely many repeated replacements
I'm looking for good practices to replace a given function recursively n times by itself with its arguments. The following example (for n=2) hopefully makes it clear:
...
0
votes
1answer
46 views
Using the Replace function [closed]
How can I replace two variables at once with Replace[] ? Can't find how to do this. I tried
Replace[x^2+y^2, {x -> a, y -> b}]
but does not work...
7
votes
2answers
123 views
Replacement Rule for Functions
Attempting to write a rule that will substitute an undetermined function of several variables by some other undeterminate functions (also, of the same several variables). I can do it in an inelegant ...
2
votes
3answers
144 views
How to avoid Replace substituting subscripts?
I have a polynomial in $\rho$ with many parameters (I will omit the polynomial code in the Mathematica expressions below because it is too long):
$$
\rho ^3 J (\mu +1) \left[(A \delta \tau _0+B (1-\...
0
votes
1answer
39 views
Substitution inside an expression [duplicate]
I'm trying to get mathematica to replace an expression with a reduced form. I wanted to replace $(k/w)$ with $h$ in a particular expression, and I've tried something like:
...
5
votes
1answer
225 views
Neglect higher order derivatives in expression
Say I have an expression of this sort:
Derivative[5][x1][t]+Derivative[3][x2][t]+x1[t]+Derivative[2][x1][t]
and so on...
I would like to ask Mathematica to ...
1
vote
2answers
48 views
Replacement rule for terms that are separated by operators?
My main problem is how one can create a "transcending between operators rule" in the same term according to the minimal example bellow.
Suppose I need to perform a replacement of the form
...
1
vote
1answer
43 views
Question about replacement and plot
I want to plug a value into the following solution which I defined.
...
1
vote
3answers
56 views
How to apply a continious substitution reduction of (-1 + 3 phi - 2 phi^3 - 6 phi^4 - 20 phi^6 + 6 phi^7 + 3 phi^8 + phi^9)//.{phi^3->1-phi^2}
I have the answer to
$(-1 + 3 phi - 2 phi^3 - 6 phi^4 - 20 phi^6 + 6 phi^7 + 3 phi^8 + phi^9)/.{phi^3->1-phi^2}$,
that is not the problem. I am looking for a method that continues to apply this ...
4
votes
1answer
188 views
Setting Some Elements in a Matrix to zero
Assuming I have the a 5x7 matrix below:
b = ((1, 4, 9, 16, 25, 4, 2), (36, 49, 64, 81, 100, 5, 1), (121, 144,
169, 196, 225, 8, 9), (256, 289, 324, 361, 400, 9, 5), (441, 484,
529, 576, 625, ...
2
votes
2answers
67 views
Elements Replacement
Please I need help on how to replace elements in a matrix with another elements. For example, I have a (5,5) matrix, and I like to replace elements from All rows and column 3 to 5, with zero. such ...
2
votes
1answer
117 views
Notation package with Traditional Form
I symbolize subscripted variables with the form TraditionalForm, to enable easy use of TeXForm as suggested here:
...
1
vote
2answers
32 views
Replacing a subset of variables in a polynomial [closed]
Let's say I have a polynomial in n variables, e.g. x^3 + xyz + z^2, where n=3 in this case. How can I replace all of the variables in the equation with a certain number?
I tried things like
...
1
vote
2answers
39 views
Replacement rule for a function and its derivative
I have this equation:
EOM1 = Subscript[x1, t, t] + ω1^2*x1 /.
Subscript[x1_, m__] :> D[x1[x, t], m] /.
x1 -> x1[x, t]
The problem with the ...
1
vote
1answer
58 views
Convert String in Expression to Integer
I have reviewed many string replacement Q&A but I have been unable to apply them to this case (MWE):
...
2
votes
0answers
26 views
Using Min & Max of an Interval in a replacement [closed]
I want to use a replacement rule to transform a list of equations. The following works as expected:
...
3
votes
2answers
96 views
Convert defined variables to rule list
I'd like to make a function that takes a list of variables and returns a corresponding rule list with the current values of the variables. E.g.
...
1
vote
0answers
40 views
Why doesn't `ReplaceAll` work in this situation? [closed]
I can work around this by using With, but it seems really odd to get the following:
...
2
votes
3answers
45 views
Using rule output as function
Im trying to define a function using the output from RSolve, however i cant get it to work properly.
I have a RSolve that output something like:
...
1
vote
2answers
59 views
Having problems with using TableForm to format a table
I want to make a table of various values of the logistic curve given by l[x_] := 1/(1 + E^((-k)*(x - \[Alpha]))).
In basic form, this is dead easy. However, I want ...
1
vote
2answers
66 views
Why does this replacement rule for imaginary unit not work? [closed]
I'm trying to replace imaginary unit in an expression with a real unit:
E^(-I y) /. I -> 1
E^(-I y)
As you can see, in ...
1
vote
1answer
41 views
ReplaceAll giving different answer than actual replacement
I have an expression, and I wanted to evaluate it for a certain value of a variable. However, /. gives a calculation error, whereas manually replacing the variable with the value succeeds. Why?
$$\...
1
vote
3answers
70 views
How to make functional rules not depend on an argument?
Consider the following:
rule = f[x] -> Sin[x]
if I now do, say:
f[y] /. rule
this does not work, because the rule wants ...
1
vote
1answer
21 views
Merging values of a list of rules where some keys occur more than once
I have a list of rules resembling
rules = {{a -> {1, 2, 3}}, {b -> {2, 3, 4}}, {c -> {3, 4, 5}, c -> {4, 5, 6}}}
How can I neatly rearrange this to ...
1
vote
0answers
45 views
Do replacement only on certain specific forms
If I want to replace, say, a with a1 + a2 in an expression, I can write
...
1
vote
3answers
86 views
Is there a possibility of adding a second condition, or an else clause to $/;$?
Let tally=RandomInteger[{0, 1}, 10];
In the code below, I'm trying to output a list where each component $C_n=\sum^n_{i=1} \text{tally}_i / n$
The problem with my ...
0
votes
1answer
64 views
Algebraic substitution for polynomial simplification
Consider a polynomial $p(x,y)$ and we want to simplify $p(x,y_0)$ where $y_0$ is a root of some other polynomial $q(y)$.
In Maple I would use something like:
...
1
vote
2answers
47 views
Question about replace command
I want to replace the common part in the equation by different value.
Here is my equation
...
2
votes
1answer
40 views
Using OverBarred variables
Mathematica does not seem to treat variables as a unit. Consider the following:
rule = a -> Function[{x}, OverBar[a][x]]
test = a[x] /. rule;
test /. rule
It ...
7
votes
5answers
320 views
Unexpected behaviour of Nothing inside List inside Association
When evaluating the following input:
<|a -> {c, d, e}|> /. d -> Nothing
I get (expression 1):
...
0
votes
0answers
18 views
Plotting multiples figures using rules [duplicate]
Consider the following:
rule = {a -> x+1, b -> x^2, c -> 3x^3+1}
Plot[{a, b, c} /. rule, {x, 0, 1}]
This, unfortunately, does not color each plot with a ...
0
votes
1answer
48 views
Replacement of the patterns in the replacement
I want to make such changes:
$(A\, p + B\, q)[i] \to A\, p[i]+B\, q[i]$
But the replacement below can not do this
...
0
votes
1answer
33 views
Expression replacement with variable exponents
I have an expression that consists of a large sum of variables of powers like:
X[1]^(2p) X[2]^2 + X[1]^2 X[2]^(2p) + X1[1]^(1+p) X[2]^(1+p) ...
Now I would like ...
1
vote
1answer
45 views
Replacing powers with ReplaceRepeated
I have question about ReplaceRepeated. Consider
$\qquad\mathsf{FullSimplify}\left[\left\{\frac{q^5-q^4}{q^5-2 q^4+2 q^2-q}\right\}\text{//.}\, \left\{q^3\to 1\...
0
votes
4answers
76 views
Implementing a Dirac Delta like function symbolically
I have an arbitrary expression where some terms are multiplied with a Dirac delta 'like' function d(x,y). For example,
e^(ax+by+cz).d(x,y).d(a,c) + e^(ax+by+cz).d(x,y)+e^(ax+by+cz)
I need to get ...
10
votes
3answers
177 views
Perform localized, evaluation-leak free replacements
Consider the following expression:
expr = Hold[
{
f[
{1, {Print@1}}
],
g[
{{{Print@1}}}
]
}
];
I'm looking for a way to ...
3
votes
1answer
101 views
“Smart” substitution of subexpressions
I have the following question.
An expression, which I want to simplify contains several subexpressions which appear quite frequently all over the place. To optimize simplification I would like to ...
14
votes
1answer
339 views
Is there a difference between Replace with parameter “All” and ReplaceAll
Here is my extremly basic understanding of Replace and ReplaceAll.
This post is also a way for me to check if I understood the mechanism behind, if you see mistakes in my explanation don't hesitate ...
1
vote
1answer
42 views
Replace an If by a combination using replacement rules
Consider the following code :
tttest = a^2 + If[a > 0, a, -a]
a^2 + If[a > 0, a, -a]
I would like to replace my If function by something like fonction @ ...
0
votes
2answers
63 views
Replacement rules with list as matching
How can I use replacement rules to match and work with a list. For example,
{1, {2, 3}} /. {{a_, b_} -> ((a + # &) /@ b)}
outputs
...
2
votes
2answers
48 views
Replace a an expression in Exponential only but not in other terms?
I want to replace the A in the Exponent only but when I use the replace rule it also replaces the Derivative of A.
...
2
votes
2answers
53 views
Expand a recursion relation
Hermite Polynoms have the following recursion relation:
$$ H_{n+1}(x) = 2x H_n(x) - 2n H_{n-1}(x), $$
which can be rearranged to be
$$ x H_n(x) = \frac{1}{2} H_{n+1}(x) - n H_{n-1}(x).$$
Is it ...
