Questions tagged [indexed-variable]
Questions about indexed variables and related alternative methods to allow assigning indexed names to objects.
53
questions
5
votes
1
answer
48
views
Assumptions about indexed variables
I am interested in the most efficient way to impose assumptions on indexed variables. In the following stylized problem, the following code
...
- 187
0
votes
1
answer
74
views
How to specify and use indexed variables of undefined quantity?
These are toy examples intended to elicit general knowledge on indexed variables of undefined (symbolic) quantity; please feel free to offer better examples.
Suppose I wish to "solve" this: $...
- 2,480
0
votes
1
answer
60
views
Replace elements of indexed list by list of rules
I have an array bs that contains many indexed elements b[ ]. I want to define the values of bs by a list of replacement rules. ...
- 740
1
vote
1
answer
70
views
Indexed array cannot be named by the name of its elements
Indexed Arrays or lists can be created by
Array[k,3]
(*{k[1], k[2], k[3]}*)
However I would like to name this list also by k, i....
- 740
2
votes
2
answers
330
views
Would it be poor advice to assign roman numerals as top variables?
For example like so.
x = 10;
xi = 11;
xv = 15;
Is there an automated way to spit these numbers out maybe 1-1000.
- 7,511
1
vote
1
answer
96
views
xAct: How to identify and split module dummy indices?
Hi I'm using the package xAct but I'm running into an issue. It seems that before using //ChristoffelToGradMetric the christoffel connection has indices (which can ...
- 21
1
vote
1
answer
105
views
Counting multiple $-sign string indices in output and replacing them by normal indices
I'm using the package xTensor in xAct. My issue is that inside a module indices are replaced by strings of the form $##### which make the final output unreadable. In a related post Print expressions ...
- 21
5
votes
5
answers
868
views
List of letters longer than the alphabet
I would like to create a list of the first $n$ letters of the english alphabet. Importantly, I would like that in case $n$ is bigger than the size of the alphabet, the letters will start repeating in ...
- 191
2
votes
1
answer
96
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Handling dummy variables 2
This is a detailed exploration of my previous post,
There was some comment by @Nasser and @yarchik, I post my module in detail
...
- 437
0
votes
1
answer
68
views
Creating and defining a family of functions with indexed variables?
I am trying to do the following: Create a list as
Table[Subscript[\[Beta], i] _, {i, 1, dim}]
And then use this list to define a function:
...
- 5,061
5
votes
3
answers
154
views
Listing all Index Possibilities Given a Vector and Indexed Set
Let's say I am given a vector $v=(5,2,-2,-4,3)^T$ and $\alpha \in \{-1,1\} $. I want to find all indices $(\alpha,i)$ such that $\alpha v_i >0$, where $v_i$ is the $i$th entry of the vector $v$ ...
0
votes
1
answer
66
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Avoiding For loops to perform an assignment to a variable with indices of user-choice [duplicate]
I am looking for an efficient way to perform the following operation without For loops
...
3
votes
2
answers
161
views
Replacing multiple variables according to the index
I'm currently working on the Polya's Enumeration Theorem implementation in Mathematica. As an example, of what I want to do, here's a formula I'm working with:
$$P_{C_{12}}(x_1,\ldots,x_{12})=\frac{1}{...
- 119
3
votes
2
answers
69
views
Solve with a non-numerical-index constant
I have 4 different constants in a given expression. Due to their physical interpretation, it makes sense to label them with non numerical indices, such as $r_+$.
The problem is that they prevent even ...
- 51
0
votes
2
answers
79
views
Extract subscript of variable in product
My input is a product of the variable x with index:
x[1]^2 x[5] x[7]
How do I extract the indices of the above product to get ...
- 13
1
vote
1
answer
249
views
How to assign values of variables with index
I'm trying to plot the following function
$V(\{r_j\})=\sum^n_{i<j,j=1}
\frac{1}{|r_i-r_j|^2}$
in Mathematica.
For the expression of this function, I wrote
...
- 11
3
votes
0
answers
130
views
Summation variables aren't recognised as dummy variables
I'm trying to write this expression
in Mathematica, and calculate the following quantity
However, when I tried the following
...
- 229
0
votes
2
answers
121
views
Indexed variable - Function that contains summation
I have the following problem:
I have a function that looks like $f(c_1 , c_2 ) = c_1 + c_2 + c_3$.
The variables are $c_1$ and $c_2$, $c_3$ is a known constant. I would like to define a function
in ...
4
votes
1
answer
145
views
Differentiation by indexed variable in equation of Christoffel Symbols
I am very new to Mathematica, and am trying to use it to compute Christoffel symbols for a certain manifold. All this requires is taking some indexed sums of derivatives, but it builds up on several ...
1
vote
2
answers
113
views
how to create a list of machine-made index names
How can I create such lists of variables:
list1={sus1[t],sus2[t],sus3[t],...,sus99[t]};
list2={inf1[t],inf2[t],inf3[t],...,inf99[t]};
Consecutive ...
- 4,823
6
votes
1
answer
216
views
Undefined Indexed Variable
I searched already a lot about indexed Variables, and it tends to be the most applicable way to use tensor notation. But I am having a hard time to solve for undefined indexed variables:
Here my ...
- 187
1
vote
1
answer
117
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Can I overload Part for specific heads (a la overloaded array subscripting)? [closed]
Mathematica/Wolfram Language newbie here.
The behavior I am after is to be able to "overload" the subscripting of me-defined objects/Heads and thereby use them as if they were ...
user75893
2
votes
0
answers
80
views
Referring to matrices with index [closed]
For exampe I have two matrices, with index 1 and 2
Mat[1] = ConstantArray[0, {2, 2}]
Mat[2] = ConstantArray[0, {2, 2}]
I wanna assign new value with
...
- 731
3
votes
2
answers
266
views
How to use a list of indexes as a variables inside a Module?
This is a trivial function, just to show that Module does not recognize the list generated by Table.
...
- 31
1
vote
1
answer
70
views
How does Mathematica evaluate sums where the upper limit of the index is not an integer?
I am interested in the way Mathematica evaluates sums where the upper limit of the index is not an integer - i.e., sums that are some sense mathematically meaningless. For example:
...
- 2,047
3
votes
2
answers
272
views
Define implicit dummy index?
I've been looking for a solution to this question for a while. I was wondering if anyone is aware of a way of defining symbolic dummy indices to implement Einstein's convention.
Let me explain with an ...
- 137
0
votes
1
answer
202
views
Subscripts use to make expression readable [duplicate]
I am trying to write a function in mathematica which depends on different parameters. For example
$$f(x_1, x_2, x_3, x_4, x_5)= 2x_1+\sin(x_2)+x_3*x_4-x_5^{-1}$$
(My actual function has 12 such ...
6
votes
2
answers
240
views
How to create a nested list of variable depth with indexed elements
i want to obtain this definition of a nested list
t = Table[C[i, j], {i, 3}, {j, 3}]
with arbitrary depth,
...
- 615
3
votes
0
answers
154
views
Parallelize import of many files
I'm trying to speed up the import of a large number of files, using ParallelTable to store them in a indexed variable, eqDump. The files are in the folder "Frames" and are named "Conf_Run.1000", "...
- 171
1
vote
1
answer
170
views
Getting a stored variable from its value
Given a numerical value, is it possible to check whether that value is stored in (or defines) some variable in the notebook?
Maybe if I could list all of the defined variables, then I could simply ...
- 4,362
6
votes
2
answers
831
views
Defining a function of arguments with sub- and superscripts
I want to define a function that takes, several, let's say two arguments, both of which have several sub- and suberscripts. For example a function might have the signature
$$ f(x_i,q_{j,k}) = \mathrm{...
- 323
1
vote
1
answer
51
views
Manipulating variables indexed by a list
I have a variable g, indexed by a list:
g[{1,1}]=11;
g[{1,2}]=12;
g[{2,1}]=21;
g[{2,2}]=22;
I would like to move things around as follows:
...
- 867
6
votes
1
answer
1k
views
Best way to write an equation with subscripts and superscripts
This post is not about a specific Mathematica problem but about to develop the best way to enter mathematical equations with subscripts and superscripts. I have a ...
- 4,823
2
votes
1
answer
837
views
xAct, xTensor: How to avoid clash of indices?
Please refer to the picture below. In the first line, I define the angular momentum vector $\vec{L} = \vec{R} \times \vec{P}$ using the Levi-Civita tensor $\epsilon^{i}_{jk}$. The definition relies on ...
- 611
1
vote
2
answers
223
views
Collecting terms from expression with indexed functions
Say I have an expansion of terms containing functions y[j,t] and its derivatives, indexed by j with the index beginning at 0 ...
- 115
0
votes
1
answer
47
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Getting named functions from an sequence of parameter values applied to a parametric function [closed]
The general question is how can I loop on names and indices?
An example:
I have
pfun = ParametricNDSolveValue[{y'[t] == a y[t], y[0] == b}, y, {t, 0, 10}, {a,b}]
...
- 1,235
0
votes
2
answers
496
views
Summation over an index and a set
I have an index CC and a set of values CM, and c is an element of CM and ...
- 4,823
2
votes
1
answer
114
views
Loop with indexed function not defined for some index values [duplicate]
If anyone cares, this is supposed to be a very simple implementation of a Metropolis algorithm for a uniform distribution. I want to plot the variance of the sampled values as a function of an ...
9
votes
1
answer
872
views
Einstein summation convention for symbolic vector calculus
I am trying to do some vector calculus in Mathematica in index notation form because it gives a clear result that can be compared to pen and paper calculations. Since there is no built in Einstein ...
- 765
0
votes
2
answers
227
views
Sum over integer partition with variable function argument
Define
$$\hat{X}(Y) = [X,Y]
$$
I have known matrices $S_i$ and $V$. I am trying to use Mathematica to define a function which calculates
$$
\sum_{\substack{n_1, \ldots, n_k>1\\ n_1+\ldots n_k = ...
- 253
1
vote
1
answer
206
views
Create list of values with arbitrary index and the use it in a function
I have the following generating functions:
$l_{2i-1}=l_{1}-(i-2)(w+s)$ with $i\geq 2$ and
$l_{2i}=l_{2}-(i-1)(w+s)$ with $i\geq 2$, so the first one is for odd index and the second for even index. ...
4
votes
1
answer
66
views
Taking a Part of a Part of a Variable
Say I have Part of a variable x.
Part[x, 1]
Then, I'll get an error message, as the ...
- 1,555
2
votes
2
answers
65
views
Naming indexed output streams
I need to write into multiple files in a Do loop.
Hence, I tried to open multiple streams:
...
0
votes
1
answer
55
views
How to truncate equation with multivariables
I am trying to set certain terms zero. How to set terms with greater than 'a3' and 'an3' zero in the following equation:
...
2
votes
0
answers
93
views
ParallelDo with doubly-indexed iterators
What is the reason that ParallelDo works with singly-indexed iterators, but not doubly- or more-indexed iterators? For example, the code
...
1
vote
0
answers
71
views
Symbolic summation with variable bounds and variable number of indices
I wish to compute compute terms like Sum[f[t[j[1]],t[j[2]],...],{j[1],m},{j[2],n},...] for arbitrary positive integer n and any ...
- 21
1
vote
1
answer
229
views
Multivariable functions symmetric in their arguments/representing indexed coefficients
Context: I have equations for indexed coefficients $C_{ij}$ which I have represented using 2-variable functions in Mathematica. e.g.,
...
- 123
1
vote
1
answer
164
views
subscript index notation select certain value [closed]
I have an indexed variable Subscript[p, s, m, t] established using the Notation method. There are various expressions where s, <...
1
vote
1
answer
70
views
How do we input powers of indexed variables?
I have tried
(a[i])^2
and alternatively
(a^2)[i]
Apparently both seem to work, but I was wondering what was the right way ...
- 79
0
votes
1
answer
179
views
How do I get Mathematica to invert a matrix with subscripts involved? (Subscript usage)
I want Mathematica to invert a matrix in which all variables are symbolic including Subscript. Now I am guessing this has something to do with the method I'm ...
- 79