All Questions
Tagged with substitute or replacement
1,686 questions
2
votes
2
answers
22
views
why replacement does not work with centerdot [duplicate]
a ** ad ** ad //. a ** ad -> 1 + ad ** a
this replacement works to move all the ad to the left of the a terms.
...
- 312
0
votes
0
answers
28
views
ReplaceAll (/.) not working as expected in Module [closed]
There is a difference between the following two expressions.
Expression 1:
...
- 11
0
votes
0
answers
71
views
0
votes
0
answers
37
views
Machine precision in ReplaceRepeated
I am relatively new in Mathematica and facing the following issue. I replace the parameters in an expression with a list of values using the function ReplaceRepeated and am getting the error: General::...
- 1
6
votes
5
answers
291
views
Trying to substitute an element of a given type by an integer
I have two lists:
a = {{0}, {0, 0, 0}, {0, 0, 0, 16, 12}, {13, 7, 11}, {14}}
b = {0, 2, 0, 2, 2, 2, 0, 0, -1, 2, 2, 2, 2, 0, 1, 0, 0, 0, 0, 1, 1, 1, 0}
The ...
2
votes
1
answer
79
views
The arrow inside string [closed]
In Mathematica, if using ->, it gets automatically replaced with a nicely looking arrow. However, if using "->", ...
- 5,963
1
vote
0
answers
43
views
How to Substitute a Metric into a Variation of the Action in Mathematica to Obtain Field Equations?
I have already calculated the variation of an action for a modified gravitational theory, and now I want to substitute a specific metric (e.g., the Schwarzschild metric) into this variation in ...
0
votes
2
answers
81
views
2
votes
1
answer
184
views
JordanDecomposition gives out different answers on symbolic and numerical calculations
Numerical substitution before or after performing the JordanDecomposition yields different results.
Here is the source code to reproduce the error:
...
- 41
3
votes
1
answer
85
views
Replacing d[r]/dt by 0 in expression
The purpose is to recognize d[r]/dt in the expression below, and to make the expression zero. It seems impossible because there is no Time[Power[dt,-1],d[r]] in the expression at the left hand side in ...
- 800
1
vote
1
answer
77
views
2
votes
2
answers
122
views
Ask Mathematica to prioritize writing an expression in terms of another
I have an old reference text with tables of solid spherical harmonics expressed in cartesian coordinates. (Edit: Here's a digital version of said table, for the curious.) In an attempt to replicate ...
- 123
0
votes
0
answers
64
views
How to Replace the expression with unknown parameters？
I do not want to do Derivative, because it will be very slow after million times.
My expression is just the Exponential as following,
...
1
vote
1
answer
76
views
How can I write a single pattern for replacement for a nonlinear change of variables
I have a polynomial in say a,b, and c, and I want this to be in terms of x,y, and z where a^(i_)*b^(j_)*c^(k_) ->x^(i+j+k+1)*y^(i+k+1)*z^(k+1), but if I try to ...
- 205
1
vote
0
answers
67
views
How can the reverse of a rule which contains two arguments be defined in Mathematica? [duplicate]
Suppose I have a rule in Mathematica:
x -> x[a] defined under some variable. Is there a way I can use the reverse of the rule ...
- 2,953
3
votes
2
answers
136
views
How to do substitution of a function by another function in derivatives [duplicate]
Simplifying my problem, I have the expression D[f[x], x], and I want to substitute f[x] with ...
1
vote
1
answer
107
views
2
votes
0
answers
66
views
Doubt about ReplaceRepeated?
I made the following code:
L={{1,2},{2,3},{2,4}};
R:=(L=(L/.{x_,y_}:>Splice[{{x,y},{x,x},{y,y}}]/;MemberQ[L,{x,y}])//Union)
When I run R three times, I get:
<...
- 5,573
4
votes
3
answers
170
views
How to map a list of elements to a list of positions of a matrix
I have an all zero matrix
zeromatrix= ConstantArray[0,{4,4}]
I have a list of non-zero positions and a list of non-zero values
...
- 891
4
votes
5
answers
222
views
Transform a list of rules into a list of function definitions
I have a list of rules obtained by solving a system of equations, e.g.
{f[x] -> a + 3 h[x], g[x] -> 2 a + c + 6 h[x]}.
I wish to convert this list of rules ...
0
votes
0
answers
36
views
How to apply dependent rules in a complex expression?
I am working with a complex expression, $L_0$, which I need to simplify iteratively using a series of dependent replacement rules. Here's the structured approach I am trying to implement:
Start with ...
- 544
1
vote
0
answers
53
views
How to Prevent Short Name Character from Auto Converting [duplicate]
The following code creates the short name character aliasdelimiter, then selects it and reads and tests it.
...
- 6,016
0
votes
1
answer
80
views
Transforming an expression into function
I want to transform the expression a = 2 x + 1 into f=Exp[a], z=Log[x], and express the ...
- 780
0
votes
0
answers
38
views
Can I remove a rule from a built-in function?
Can I remove the rule DiracDelta[n x]==DiracDelta[x]/n when n is numeric from the definition of ...
- 3,712
0
votes
1
answer
30
views
0
votes
2
answers
68
views
Hold Dt[r,t] unevaluated but Mathematica substitutes value of r
I have the formula for the Volume of the sphere and then differentiate
Dt[V == 4/3 \[Pi] r^3, t]
The output is
...
1
vote
0
answers
113
views
Perturbation theory. Get xAct tensor component. Substitution for xAct tensors
I work with perturbations in FLRW metric with arbitary curvature. I'm following Weinberg's book.
In modified gravitation theory there is additional tensor S and I need to find it's perturbation in the ...
1
vote
1
answer
58
views
How to achieve automatic nesting of pattern application
I want to apply the following rules:
...
- 2,182
4
votes
0
answers
140
views
Limit of a PolyLog does not work [bug]
This is an issue I am having with Mathematica version 13.1.0.0. I tried the following code, but it does not work as expected:
...
0
votes
1
answer
36
views
Cross derivative rules
I am trying to generalize the condition
Derivative[1, 0][ℒp][t, ϕ] -> Derivative[0, 1][ℒp][t, ϕ]/l
for $\ell$ a constant, through the following rule
...
- 155
3
votes
2
answers
181
views
Modify Rules with new patterns
My Rules always have one instance of TR on the LHS, and several on the RHS, like this
TR[2] -> TR[5] + TR[h, g]
I want to generalize them by adding optional ...
- 1,122
1
vote
1
answer
59
views
Weird behavior when using Parallelize with LieART
I want to perform computation with the LieART package and Parallelize some long computation. But I run into the following ...
- 555
1
vote
0
answers
40
views
Replacing an expression with pre-defined function
I am asking Mathematica to do a long calculation with functions I am defining at the beginning of the script. Because the resulting expressions are long, I want to replace them with the functions I ...
- 111
3
votes
1
answer
100
views
Sort the arguments of a function using replace
I want to sort the arguments of a function f while multiplying with the signature of the permutation, i.e. f is totally antisymmetric function. My idea was something like
...
- 187
2
votes
2
answers
106
views
Why does Replace function not work the first time I try it?
Please explain why in the following mathematica code, the cos term was not replaced in the first try, but got replaced in the second try?
...
- 121
2
votes
4
answers
320
views
Ignore higher order terms in an expression
I am trying to ignore terms that are higher order (third or more) in an expression. For example, for the input function:
$$f_{in}= \alpha\beta + \alpha^2 + \beta^2 + \alpha\beta^2/2 +
\alpha^2 \beta $...
- 123
0
votes
0
answers
55
views
Mathematica solve with conditions on constants differ from replace
I have been trying to solve some complicated linear equations in Mathematica, with variables $y_{i}$, and constants $a, f_{j}$ where $0\leq j\leq10$. I only care about the case where $\sum_{i=1}^{10}...
- 101
4
votes
1
answer
128
views
How to write a rule that matches alternatives but return one of them always?
Consider the following rule:
$rule={"Period ID"|p:"Period":>p};
This rule will match ...
- 9,751
3
votes
1
answer
108
views
How to `Collect` where `var` is one expression?
Edit:
Clear["Global`*"];
expr1 = (a + c - b + 1)^3 + (-b + a + c + 2)^4 // Expand
For test case expr1, this is the ...
- 2,067
0
votes
0
answers
38
views
Replacement not working as desired [duplicate]
The following replacement works fine
ReplaceAll[1/F[x],F[x]->y]
(*1/y*)
but this doesn't
...
- 343
6
votes
4
answers
348
views
Transform sequence into ragged list
I want to transform
seq = {x, 1, 2, x, 3, x, 4, 5, y, y, 67, y};
into
{1, 2, {3, {4, 5}}, 67}
The only way I found is rather ...
- 83.1k
0
votes
1
answer
89
views
Why does Mathematica fail to substitute some terms in an expression but not others?
I have an expression of the form:
$A-\frac{e^{-t/t_1} \; a \; b}{c \; t_1} \; U_1 - \frac{e^{-t/t_2} \; a \; d}{c \; t_2} \; U_2 -\frac{e^{-t/t_2} \; a \; e}{c \; t_2} \; U_2 - \frac{e^{-t/t_3} \; a \;...
4
votes
4
answers
309
views
Replacing string values with one of the sequence-functions
Given the following list of rules (which might contain duplicate
keys), I want to replace the string values with the first preceding numerical value.
...
- 83.1k
1
vote
0
answers
43
views
Why list of replacement does not work in the following example? [closed]
I want to replace a long list but in the following format, but it does not work:
(Aa + Bb + Cc) /. {{Aa, Bb, Cc} -> {x + 2, y + 2, z + 2}}
- 575
1
vote
0
answers
59
views
Replacement rule runs for a long time [duplicate]
I have a simple expression that reads (some expression in b) q^(8/3):
...
- 555
1
vote
1
answer
42
views
How to do this replacement? Match the variable, but not the function [duplicate]
I have the following expression:
$$\frac{\left(-2 \lambda \lambda [\theta ]+\lambda [\theta ]^2+\lambda ^2+\lambda \right) \lambda '[\theta ]^2}{\lambda [\theta ]^2}$$
I want to replace every ...
1
vote
0
answers
43
views
Difference in pattern matching between Cases and ReplaceAll (Already searching at all levels and heads)
Why is there a difference between the pattern matching between Cases and ReplaceAll in the following:
...
- 4,781
1
vote
0
answers
63
views
Random replacement in array
In the spirit of this interesting article of Stephen Wolfram I also decided to study some issues related to mutations.
I’m working with simple {0,1} arrays and I’ve ...
- 1,924
1
vote
1
answer
83
views
How to replace C[1] in solutions of trigonometric equations into k?
This is my code
Table[{HoldForm[Cos[3 x + 2 Pi/5]] == Sqrt[i]/2,
Reduce[Sin[2 x] == Sqrt[i]/2, x, Reals]}, {i, 0, 4}]
How can I replace C1 to ...
- 1,796
3
votes
2
answers
105
views
Multiple replacements in a long expression
Why does the replace /. not work on the second argument in the following expression:
...
- 575