Questions on the manipulation of List objects in Mathematica, and the functions used for these manipulations.
7
votes
1answer
78 views
Ordering function with recognition of duplicates
Fairly often I have a need to get the Ordering of an expression but with recognition of duplicates. For example:
...
17
votes
3answers
364 views
How to efficiently find positions of duplicates?
Is there an efficient way to find the positions of the duplicates in a list?
I would like the positions grouped according to duplicated elements. For instance, given
...
0
votes
3answers
125 views
How to construct pairs in a list?
I have an expression like this,
input = x[1] x[2]^3 x[5]^2;
Fist step, we can get a list from the input expression,
...
5
votes
4answers
204 views
Prevent Part[] from trying to extract parts of symbolic expressions
If you have a list, e.g.
{1, 2, 3}
then you can extract the $k$th part using Part (...
10
votes
3answers
446 views
What is Mathematica's equivalent to MATLAB's filter function?
The MATLAB code
filter(0.5,[1, -0.5], [1:10])
is equivalent to
Rest@FoldList[(#1 + #2)/2. &, 0, Range[10]]
I don't ...
3
votes
4answers
209 views
Extract function arguments
Is there a way to extract the arguments of a function? Consider the following example:
I have this sum
...
9
votes
2answers
210 views
Speed up 4D matrix/array generation
I have to fill a 4D array, whose entries are $\mathrm{sinc}\left[j(a-b)^2+j(c-d)^2-\phi\right]$ for a fixed value of $\phi$ (normally -15) and a fixed value of $j$ (normally about 0.00005). The way ...
3
votes
2answers
150 views
For loop with steps other than 1
I would like to do a For loop with a jump 2*Pi instead of 1.
For[j = 0, j <= nmax, (incr = 2 Pi), ...]
Actually what I want to do is ...
2
votes
1answer
43 views
Replace a specified portion of an array with elements from another smaller array
This may be a trivial question, but I have been at it for a couple of hours and I have not made much progress.
I have a 10 x 10 array (T) that I have used to generate an 8 x 8 array (Q). I want to ...
12
votes
9answers
346 views
Dropping n consecutive terms from a list periodically
Suppose I have the following list
lis = Range[100];
and I want to remove n consecutive terms periodically from the list. For example suppose I want to drop terms ...
2
votes
3answers
211 views
How make f[{x,y}] evaluate as f[x,y]?
I frequently encounter the situation where I have a function of two real variables defined, e.g.:
f[x_, y_] := 9 - x^2 - y^2
But then I need to feed into ...
1
vote
1answer
111 views
1
vote
2answers
92 views
Subtract more than one array using DeleteCases
I need to create an array subtracting two arrays from another array. I know how to subtract one:
am = DeleteCases[amp, Alternatives @@ af]
I can subtract an ...
1
vote
2answers
133 views
Select rows from table by keys
I am looking for a way to iteratively select all sublists with the same ID (my 1st column, residual columns are AbsoluteTime entries). First, I obtained the list of ...
8
votes
1answer
220 views
How to remove some elements in a list based on a rule?
I want to deal with the following list.
mylist = Table[cof[i] exp[i], {i, 1, n}]; (*n is very larege *)
exp[ ] is a function ...
-8
votes
1answer
210 views
Plotting Energies vs. m for all values of R with the colors of the levels indexed by R [closed]
I have two lists like this:
...
0
votes
0answers
36 views
Correspondence between eigenvectors and eigenvalues [duplicate]
Let us say I have a matrix h (2x2). Now, I want to get the eigenvectors and eigenvalues of my matrix h:
...
4
votes
3answers
246 views
Separating positive and negative numbers into two arrays
$c$ is a vector with real numbers.I want to separate the positive ones and the negative ones into two vectors: $a$ and $b$.
I have the following problem:
When I do:
...
2
votes
2answers
262 views
Finding a best fit curve and plotting it [closed]
I have a list as shown below:
m01 = {{250, 0.083121}, {200, 0.0888446}, {150, 0.0992422}, {100, 0.121567}, {50, 0.186825}}
I'm new to Mathematica, and would like ...
0
votes
0answers
65 views
0
votes
1answer
62 views
Collecting roots of different equations and create a list
I solve two equations and have two solutions one by each equation. I want to create list of these roots. Could anyone please help me? Appreciate it.
m02R150 = FindRoot[P1 == 0, {E1, 0.07, 0.1}]
...
4
votes
2answers
126 views
Extracting data from a table under conditions
I have a very large table with two columns. Let's say the name of first column is E and the name of the second is P. How can I get the E values when P = 0.
3
votes
1answer
92 views
How can I get a single solution to a set of inequality constraints?
I have a set of constraints to which I require integer solutions. However, instead of needing all possible integer solutions (as obtained by using ...
1
vote
1answer
62 views
Calibrating Precision in calculations
As the title says, I encounter an irritating problem which has to do with the accuracy or the precision used in the calculations. To be more specific, I have the following code:
...
1
vote
0answers
105 views
Transferring a list from one notebook to another
I have Mathematica code split into two notebooks. The first part is supposed to run and output a list of numbers into a text file, using Export. The second part ...
6
votes
2answers
202 views
removing elements that are contained in other elements
For example, I have a list of lists:
l = {{a,b,c},{a,b,d},{d,e},{d},{a},{a,b},{f}};
And I want to remove all the lists that are contained in other lists:
...
6
votes
3answers
130 views
How to 'merge' a list like FromDigits, but with a mixture of numbers and symbols?
How do I go from {C,4,G,5,S,7} to C4G5S7
5
votes
1answer
160 views
Problem with creating a large list of tuples
This is a follow-up question from Sum of Multinomial Coefficients
I have thought about the meaning of the formula I mentioned and, with help, I implemented the following code:
...
9
votes
7answers
319 views
6
votes
2answers
167 views
Merging two Lists
I have two tables. One is given by
T1 = Table[{x, y, 0.}, {x, 0, V},{y, 0, V}]
and from a calculation I have the second, a list of points {x, y, z}
...
2
votes
4answers
243 views
Mapping over the last level of a list, or equivalent operations
I would like to style each element of my list using Style. But when I try
...
6
votes
1answer
325 views
Get the coordinates from ContourPlot and RegionPlot
How do I get the coordinates from a contour plot I've done in Mathematica? For example, I have a two-variable function f[x, y], for which I can make a contour plot:
...
13
votes
3answers
286 views
Quick multiple selections from a list
What is the fastest way to make multiple selections from a list? Compiled methods included.
For example, here are two methods for selecting a subset, compared:-
...
2
votes
1answer
203 views
How to solve equations self-consistently
I want to solve the following equation self-consistently. So,
H.u = e.u
{{1, d}, {d, 1}}.{u1, u2} = e.{u1, u2}
I guess an initial value for ...
-1
votes
1answer
74 views
How to separate a vector into two vectors, one having the first half of my original vector and the other having the second half
I have a set of n vectors with an even length. Let us make an easy example with 3 vectors of length=4:
...
1
vote
1answer
106 views
Creating an array eval [closed]
How can I create an one dimensional array (a vector) evaluating a function of two variables? I know how to do it with one variable:
Array[f, n, {a, b}] generates a ...
1
vote
3answers
108 views
Separate an array in two arrays, the even and odd terms being separated in these two arrays
How can I separate the odd terms in one array and the even terms in another array,i.e., go from
a={1,2,3,4}
to
aeven={2,4} ...
-2
votes
1answer
132 views
Non-regular grid data
I have issue with non-regulary spaced data. I have set of 3 numbers {x, y, z} in my list.
...
6
votes
1answer
276 views
Remove redundant brackets. Clean up lists
There are numerous examples whose end result is the removal of empty brackets "{}" and empty lists here, I still can't find an example of simply removing redundant brackets though.
(It's hard for ...
1
vote
3answers
179 views
Loop through a list and select elements
I am new to Mathematica and I have no idea how to make a basic for loop work. I want to loop through the elements of a list: Range[45, 200]. I want to select the ...
0
votes
1answer
61 views
How to get a number, but not a list, of the dimension of your array?
I need to use the dimension of a certain array, to use it as a bounder in a loop afterwards. The problem is that I get a list, when write :
...
3
votes
5answers
239 views
How to combine some elements of a list?
In order to simplify my expression, I face a list manipulation problem.
For example, given the input list
...
9
votes
1answer
169 views
Creating a number based on given conditions
In the grade 7 math curriculum here in Alberta we teach divisibility. I'm trying to write a program to create questions based on the idea of a student being given say, 4 digits, and then choosing ...
0
votes
1answer
150 views
Find Roots in Do loop
Task: Finding roots in loop
t = List[1, 2, 3, 4, 5]
fx[x_] := a*x^2 - 5
List[Do[Print[FindRoot[fx[k] == 1, {a, 1}]], {k, 0, 5}]]
Output: Currently the output is ...
5
votes
3answers
154 views
Elementwise join
I have two tensors of arbitrary but equal rank n (and equal dimensions): A and B, and I want to get a third tensor of rank n + ...
4
votes
5answers
121 views
Convert a list with three arguments {x0,x1, step} into an equidistant table?
How can I convert a list such as:
a = {1, 2, 0.1}
into sequence so that I can pass them into a function, e.g. I want to be able to do something like this
...
2
votes
3answers
170 views
Selecting subsets of a list containing a specific element
I'm trying to generate all the subsets of a set containing a specific element.
For example, for the set {1, 2, 3, 4}, with the specific element I want inside each subset being 4, the required answer ...
2
votes
1answer
103 views
7
votes
3answers
137 views
Multiply a list of matrices by a list of vectors
How does one multiply a list of matrices by a list of vectors, elementwise? For example, multiplying
...
3
votes
2answers
96 views
Sequence and boolean And
I'm trying to figure out if a calculation result it's a valid result. As it return a matrix, I need to test that every element it's a number, so I thought this could work...
...
