Questions tagged [index]
Questions about functions with intrinsic part index such as SparseArray, Part and Indexed or iteration variable indexes such as MapIndexed, Sum and Product.
100
questions
1
vote
2
answers
71
views
Can't use iterative variable as part specification [closed]
I've got the following mathematica code:
...
- 11
2
votes
1
answer
64
views
Problem with integration with indexed variable
I wonder why I can not have a correct integration form on Mathematica with some indexed variables.
Indeed, when I write :
...
- 23
3
votes
2
answers
152
views
How to use Position to select based on absence of a pattern?
I need to use Position to obtain positions of entries in list of lists that do not contain a certain pattern.
The problem is that ...
- 137k
5
votes
3
answers
142
views
Substituting the element of a list into a list that contains the index position
I see similar questions for lists and indexes and manipulating with Thread, MapIndexed,etc., but I do not see how to do a substitution.
I have a list of coordinates for a geometric object and a list ...
- 55
1
vote
1
answer
138
views
Is there a builtin command or a workaround to generate a nested sum (of apropriate level) from an expanded expression?
I have the following output from some Mathematica manipulation of nested sums. Does Mathematica have a command or combination of commands that recovers nested sums from the expanded form?
$$\begin{...
- 153
0
votes
0
answers
39
views
One as Subscript and Supersripts
I am trying writing code with a lots of symbols and their products.
There is an issue with the appearance of "1" as an index. e.g.
Subscript[[Delta], 1 n]
Why "1" does not appear ...
- 331
0
votes
1
answer
70
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. ...
- 563
4
votes
3
answers
352
views
How to replace the element in list of list by its ordering index
I have a list of list: res={{9, 1, 5}, {3, 6, 12}}
I want to change it to res={{5, 1, 3}, {2, 4, 6}}
by following their ordering ...
- 95
6
votes
4
answers
647
views
Find min and max indices of highest and lowest elements in sorted list
I have a list of integers of the form
...
- 239
0
votes
1
answer
38
views
index as an attribute for a function containing data frame
Two questions. I have created a sample problem, and would be glad to have your help.
I have 2 functions, fun1 and fun2, and one ...
- 877
2
votes
3
answers
183
views
How to include index for the coefficients in series or sequence
I am trying to use the "Summation" command for the exponent and for the corresponding subscript of the coefficient, but it fails. See the example below:
...
- 331
2
votes
0
answers
345
views
Part::partd: Part specification is longer than depth of object (Simple list) [closed]
I know that this question has already been asked (I searched for answers), but in every thread I saw the code was much more complicated than what I'm trying to do, and I can't understand why this ...
- 31
2
votes
0
answers
168
views
Map a function that uses the lists indices as arguments
Suppose I have a function f[x_] that I want to Map over somelist (assumed to be one ...
- 65
4
votes
2
answers
112
views
RSolve solves only one of two equivalent recurrences
I am having an issue with the RSolveValue/RSolve function. Specifically, Mathematica is able to correctly evaluate ...
- 41
3
votes
2
answers
77
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
3
votes
1
answer
91
views
Summing list elements for given index tuple
Is there a more compact way of summing certain elements of lists together when given a tuple of which elements to sum. For example if I am given the list of size 8:
...
- 295
0
votes
0
answers
27
views
How to define an index list of local variables for arbitrarily long
Suppose initially I have a list that looks like
list1 = {A, B, C}
where the elements A, B, C are all matrices. I want to substitute all the three elements by list1 ...
0
votes
2
answers
164
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 ...
3
votes
2
answers
128
views
Re-defining the built-in `CharacterRange` for a range of 1500 or more
I have the following function (developed by @kglr), and now I need to use the same function with a list of 1043 characters rather than a limited number from A to <...
- 5,470
6
votes
1
answer
266
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
123
views
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
3
votes
2
answers
84
views
Index of item inside StructuredArray
How do I extract position of item in StructuredArray without converting using Normal?
The following code finds the position of ...
- 9,578
2
votes
3
answers
182
views
Split matrix expression into multiple lines
Given a matrix expression
testm = {a + b, c + d, e};
{# , testm[[ # ]] // Simplify} & /@ Range[ Length[testm] ] // MatrixForm
\begin{equation}\begin{pmatrix} ...
- 201
2
votes
1
answer
80
views
Fancy Indexing of a 4D array (tensor)
I'm trying to mimic the CoefficientArrays function, which I can't get to work for my symbolic equations. The CoefficientList ...
- 127
4
votes
1
answer
335
views
How to get the class of neighbors in a 2D periodic matrix?
I'm trying to analyze the spatial structure of some rectangular arrays by counting the number and class/type of neighboring points around every point in the arrays, with periodic boundaries.
For ...
- 1,593
3
votes
2
answers
264
views
Labeling elements of a table
I have a table of the form(the table is very long, i put an example):
tab1={{{1,10,30},{1,20,54},{1,30,65}},{{2,10,35},{2,20,65},{2,30,70}}}
How can I give ...
- 97
1
vote
1
answer
690
views
How do I evaluate my functions over a range of values? [closed]
I want to use the list of data which will come from MapData1 (in code); the first element is θ and second is Action(I). I want to use this Action(I) and Angle(θ) in ...
- 35
3
votes
0
answers
149
views
Efficiently get positions of Query results
I have some very large Datasets. Is there any efficient method of getting the positions of results found in a Query? That is, without using ...
- 3,581
0
votes
2
answers
47
views
Arrange exceptions in a list by some criteria
I have some dataset, which is supposed to have $30000$ in the last column, and I want to find the elements that break this, and arrange them numerically while mantaining the index. What I'm currently ...
2
votes
1
answer
337
views
how to add labels of points next to it based on index in ListPlot
I have a list of some points. I plotted each point and its closest surrounding points.
...
- 111
6
votes
2
answers
1k
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{...
- 333
7
votes
1
answer
119
views
How would you explain Nothing[] weirdness? [duplicate]
I would like to use Nothing[] to make some elements of a list invisible. (The intended use is to remove a few unwanted points from a ...
- 164
1
vote
1
answer
113
views
How does Indexed work in terms of sparse array
I want to use indexed given that s is an element [0,500] but I am unsure how to write that without getting a format error or a tensor error.
...
- 11
0
votes
1
answer
124
views
Integer functions indices in a sum
I have some troubles with plotted A versus p, especially for the function F(s,l,p), I don´t know how deal with the integer functions indices of the sum. How can I input such a sum to Mathematica?. ...
- 19
14
votes
2
answers
1k
views
Map vs. Table for index-specific operations on 2D arrays
Many experienced users on this site tend to use Map (and its variants, MapAt, MapIndexed, etc.) rather than Table. When applying the same operation to every element of an array, Map does seem more ...
- 3,603
10
votes
3
answers
249
views
Function over a list that depends on the index
Suppose I have a list
{a, b, c, d}
I want to operate on this list with a function which depends on the index of the element, e.g. I want to add the index ...
- 213
3
votes
3
answers
889
views
Is there an easy way to index by a binary vector / mask?
I would like to be able to extract elements from a list where indices are specified by a binary mask.
To provide an example, I would like to have a function ...
- 777
1
vote
2
answers
244
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
2
votes
0
answers
113
views
Typography of Mixed Tensor Index Notation
How can one properly and quickly write a mixed "tensor" such as $\Gamma{}_{1}{}^{2}{}_{3}$?
Shortcuts such as esc Gamma esc, Ctrl+^, Ctrl+_ are prefered. I intendd to use this in an inline equation ...
- 1,853
1
vote
1
answer
236
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. ...
1
vote
0
answers
660
views
Sum over multiindex
I would like to calculate a sum over some multi-indices, that follow a specific pattern.
$$\sum\limits_{1\le i_1<i_2<...<i_k\le N} A(k,i_1, i_2, ..., i_k).$$
$A$ is a fix expression of the ...
- 11
0
votes
0
answers
20
views
Why do I have to index my covariance matrix as if it has 3 dimensions [duplicate]
The language reference for getting parts of a matrix seems to make sense. I'm wondering why my covariance matrix behaves differently.
...
- 101
2
votes
0
answers
113
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
...
0
votes
0
answers
48
views
Defining list of data
I need to define a list of parameters A[i] where i runs from 1 to some integerN. The ...
- 417
0
votes
2
answers
123
views
Algorithm for Swapping indices and simplifying the summand in a double sum [closed]
Say we have something like
$$ \sum_{p}^N\sum_{q}^N \cos(p) \sin(q) - \cos(q)\sin(p) $$
usually, in the case like this, the indices p and q can be swapped, and the sum simplifies to 0.
I have an ...
- 121
3
votes
2
answers
659
views
Indexing nested list with another list
So I'm wanting to index the sublists within a list using another list.
So I have
x = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}}
And I want the 2nd term of the first ...
- 165
1
vote
2
answers
1k
views
Finding the x-value corresponding to a y-value found using Nearest [closed]
I have a large 2d array of infinite precision named "data" of x values and y values. I am using Nearest to find the y-value closest to a specified number, say 0....
- 11
1
vote
1
answer
177
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, <...
3
votes
0
answers
73
views
Part[] for multi-index array [duplicate]
If I want to set element (i,j) of two-dimensional array X to 0, I can write X[[i,j]] = 0. My question is how can I achieve this if I have the indices i and j in a ...
- 41
8
votes
2
answers
906
views
Add Index to All Elements of a List
My goal is to add an index to all elements of a list in the form {"a", "b", "c", ... }, so it becomes ...
- 243