Questions about Mathematica's rule-based replacement functionality, including functions such as Rule (->), Replace, ReplaceAll (/.) and ReplaceRepeated (//.).
3
votes
1answer
101 views
Pattern matching a multivariate derivative
I can extract the parameters of a single variable derivative with the rule
D[f[x], x] /. Derivative[order_][fcn_][variable_] ->
{order, fcn, variable}
...
3
votes
1answer
108 views
Set promotes Rule to RuleDelayed?
In mentally building a model of how Mathematica works, I naively expected Set to create a Rule in a symbol's ...
3
votes
1answer
75 views
2
votes
2answers
175 views
How to do substitution of variable with power in Mathematica?
I want to replace $x^{i+1}$ with $z_i$.
EDIT:
I have some latex equations, and wish to import them to MMa.
How to replace x_i (NOT $x_i$) with $x[i]$
But it seems the underscore "_" has a special ...
2
votes
1answer
90 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 ...
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 ...
2
votes
2answers
88 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:
...
2
votes
1answer
88 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:
...
2
votes
1answer
46 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
128 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 ...
2
votes
1answer
136 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, ...
2
votes
2answers
78 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+ ...
2
votes
2answers
89 views
2
votes
1answer
93 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: -
$$k^2-2 k x+x^2$$
...
2
votes
1answer
119 views
#[[1]]//FullForm = 1?
I have a set of symbolic algebraic expressions that I'm trying to get some speed into. To illustrate the issue, I'll use a simple form like { k0 X, k1 Y, k1 Z}, ...
1
vote
2answers
117 views
Using patterns in ReplaceAll to extract elements from tuples at arbitrary depths
Please consider the following:
I need to extract from MyList all last parts of each 3-tuple.
...
1
vote
3answers
149 views
1
vote
2answers
138 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.
...
1
vote
4answers
139 views
Extracting RHS from Rule
In an example from another question, the rhs of a list of rules can be simply extracted:
...
1
vote
2answers
130 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 ...
1
vote
3answers
243 views
How to manipulate nested expressions?
I have the following expression, only slightly complicated, and I'd like to do two things:
Plot the elements of the lists (though messy, all are in the same
...
1
vote
1answer
718 views
Converting polar coordinate expression to cartesian coordinates
An intermediate step in my analysis requires me to work in polar coordinates, but I would like to convert the results back into cartesian coordinates. The conversion is very simple but tedious for ...
1
vote
3answers
77 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 ...
1
vote
1answer
82 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
1answer
62 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 ...
1
vote
0answers
61 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
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 ...
0
votes
2answers
58 views
Replace expression using a tuple
Given an expression in x, y, z (for example), and a list with three elements, like ...
0
votes
2answers
69 views
Extract a List of Co-ordinates from a List of Complex Solutions
Let's say I have this list of solutions from a previous computation:
...
0
votes
2answers
56 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:
...
0
votes
2answers
75 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
83 views
Apply rule only if applicable? Check rule applicability? Custom unapplicable rule?
How to avoid recursion in the following example?
...
0
votes
1answer
68 views
What exactly happens when adding a Blank after a built-in function used in the rules of ReplaceAll?
Well, this question is just for curiosity, personally I never use ReplaceAll like this:
...
0
votes
1answer
87 views
Numerical rule evaluation -> {True, False} to deviation of target equation
I solve some equations numerically with FindRoot[] returning a quadruple {1,2,3,4}.
Because the solver sometimes do not find any roots depending on parameterization of these equations I select only ...
0
votes
1answer
114 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 ...
0
votes
1answer
72 views
Problem with Replace rules [closed]
I am struggling with a Project Euler problem with Mathematica, what I want to do is to Replace a list like this {5,6,x,x,3} with the rule {x -> i} to {5,6,0,0,3},
{5,6,1,1,3}etc,and here is my code:
...
0
votes
1answer
150 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
1answer
65 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. ...
0
votes
1answer
143 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
2answers
83 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 ...
0
votes
1answer
93 views
Extract a value from a list of InterpolatingFunction
By running the code
n = 5;
U[t_] := Table[Subscript[u, i][t], {i, 0, n}];
lines = NDSolve[{eqns, initc}, U[t], {t, 0, T}]
I get the output
...
0
votes
1answer
451 views
Plot is not showing [closed]
I've used Wolfram Mathematica 8 Trial version for two days. Any pointers are appreciated. Thanks in advance!
EDIT: There are supposed to be 4 plots, but only 3 are showing. Everything works except ...
0
votes
0answers
49 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
...
0
votes
0answers
81 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:
...
0
votes
0answers
30 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 ...
0
votes
0answers
103 views
How to apply rules to the elements of a sparse array? [closed]
I have two text files that I am importing, one is a sparse array of format {large row index,column,value1} and the other is {large row index,value2}. The row values are a small subset of a much larger ...
