Questions about Mathematica's rule-based replacement functionality, including functions such as Rule (->), Replace, ReplaceAll (/.) and ReplaceRepeated (//.).
0
votes
1answer
104 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
46 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:
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5
votes
2answers
92 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
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1
vote
1answer
81 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
147 views
1
vote
0answers
56 views
Using Root for numerical evaluation [closed]
In my expressions I have a lot of roots to calculate. For example:
Root[#1^3 + #1^2 + #1 &, 1]
Since most of them cannot be solved analytically, I would like ...
1
vote
1answer
57 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
3answers
204 views
Replace operators
/. can be used to replace variables but how can one replace operators.
For example in a * b, ...
2
votes
2answers
77 views
4
votes
2answers
67 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
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6
votes
2answers
137 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
84 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
63 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
100 views
Generating replacement rules programatically
I would like to generate sets of replacement rules programatically for predefining some permutations. So a function
...
5
votes
6answers
270 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
45 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
98 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
36 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
72 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
91 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: -
$$k^2-2 k x+x^2$$
...
7
votes
2answers
147 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 ...
0
votes
0answers
78 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
164 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:
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0
votes
2answers
62 views
Converting a list of replacement rules into a list of real values [duplicate]
The following command outputs a list of replacement rules.
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0
votes
1answer
62 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. ...
1
vote
2answers
133 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
92 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 ...
2
votes
2answers
127 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 ...
1
vote
2answers
122 views
Generating a list of rules [closed]
This is my first time asking a question on this forum.
I would like to generate a list with a range of numbers and use this list for a function to read from. Ok, now for the good part, it would look ...
0
votes
1answer
134 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 ...
