Questions tagged [expression-manipulation]
How to manipulate expressions structurally, not necessarily complying with the rules of algebra.
525
questions
3
votes
2answers
109 views
Group symbols by a given partition of the occuring symbols
I have following expression
$$-3 b_{\sigma _d}-3 b_{\sigma _v}-b-b_2+2 j-2 j_2-2 j_3+2 j_6+12$$
Mathematica input
...
0
votes
0answers
50 views
How to use replace for only one term in a long expression in Mathematica?
I am doing some Cauchy integration and in some intermediate steps I have something that looks like that:
(..many_terms...+I*\epsilon(k1-p1))/k1
where ...
0
votes
0answers
38 views
Why does Refine not use transformation rules for a user-defined function?
I defined a transformation rule for a symbol L that takes a sequence of numbers
...
1
vote
1answer
42 views
Generating examples by applying conditions to symbolic expressions
For example,
Given a list of symbolic expressions:
...
0
votes
0answers
28 views
Obtaining part of an expression from a position [duplicate]
I would like to recover a subexpression from its position in the expression.
For instance:
Position[{3, {3, 5, {6}}}, 6]
returns the position of 6 in the ...
0
votes
0answers
56 views
13
votes
1answer
541 views
How can I obtain a complete list of the kinds of atomic expressions in the Wolfram Language using only the language itself?
I mean, Wolfram is a language--it's words are infinitely combinable. According to answers to my last question, the only way I can find out if an expression is atomic is actually use the expression.
...
1
vote
2answers
66 views
How can I ask the Wolfram Language to tell me if a hypothetical expression with a particular head would be atomic or not?
Integers in the Wolfram Language are atomic expressions, while uses of the Map function are not atomic.
But if you didn't know this, how could you find out using only the Wolfram Language? The best I ...
1
vote
3answers
101 views
Why do atomic objects like 56 have a head if they're supposed to be, well, atomic?
This question follows from this one I made earlier.
If you ask for FullForm[4] you will get back 4, and that's fine. ...
0
votes
1answer
35 views
Selectively changing precision while leaving integers and rationals unchanged
I didn't find an answer to this question on the site, but as I was writing up my question, I figured out how to do it, so I thought I should post it and answer my own question so that others can ...
0
votes
0answers
37 views
Manipulation using `Together[]`
The use of Together either cancels the common factor from numerator and denominator or multiplies them with a common factor.
In my code I do not want that ...
4
votes
2answers
116 views
How to import latex matrices into Mathematica?
I have a lot of $\LaTeX$ matrices, and I want to find their eigenvalues and eigenvectors.
I tried to import them to Mathematica with:
...
2
votes
1answer
30 views
Expression manipulation with exponential
I have the following expression
a + b + c + x + y + z + r*E^m + s/E^m + t*E^n + u/E^n
I want to extract the coefficients of exponential terms as well as the ...
5
votes
3answers
217 views
Iterate over deepest values in a nested Association
Is it possible to iterate over the values of the deepest layer of keys in a nested association? For example:
...
0
votes
1answer
88 views
Need help in understanding what Extract does
Can anyone explain two examples from the Mathematica Documentation Center reference page on Extract? One is:
...
4
votes
3answers
88 views
Applying functions to leaves of nested list structure, when these leaves are more complex expression trees [duplicate]
Is there a way to apply a function h to the following nested list
{{a, b}, {c, d}, {{d, e }, {f, g}}}
where this should should become
...
4
votes
1answer
47 views
Dimensions of list used in test
I would like to reduce the number of brackets in a list for nested lists containing 1 sublist. For instance {{1,2,3}} should become ...
1
vote
3answers
30 views
Grouping expressions by associative equivalence for a single operation
I would like to group expressions under associative equivalence, but only for a specific operation used in the expression (not for other operations).
Say we have two binary operations A and B ...
2
votes
1answer
58 views
How to decompose an expression into basic forms (e.g. a[[1]] to Part[a, 1], a=1 to Set[a, 1], etc.)? [closed]
Is there something I can call in Mathematica to figure out the composition of a given expression?
I want everything decomposed to the most basic f[a, b, c] format.....
2
votes
2answers
55 views
Groupings over non-atomic elements
I use groupings as below:
Join[
Groupings[IntegerPartitions[3], {A -> {2, Orderless}, B -> {2, Orderless}}],
{x}]
Which generates:
...
1
vote
1answer
27 views
Groupings: orderless version?
Consider the following groupings code:
Groupings[IntegerPartitions[3], {A -> 2, B -> 2}]
This generates:
...
0
votes
3answers
86 views
How to simplify an expression by substitution?
Sometime Solve and DSolve give a finial form of the solution, which is fine in may applications. However, in some cases, one may ...
4
votes
4answers
128 views
Neat redistribution of association values
Given an original association:
original = <| "a" -> {a1, a2}, "b" -> {b1, b2}, "c" -> {c1, c2} |>
and a set of redistribution rules e.g.
<...
5
votes
2answers
125 views
How to write down a product with omitted terms?
I have the following term which I would like to express correctly in Mathematica:
$$
\prod_{j=1,j\neq i}^m(\rho_i-\rho_j)
$$
Can you please help?
0
votes
0answers
56 views
Collecting the derivatives of a sum
I have an expression where thereare many terms that involve the sum of the derivatives of two functions like
$\qquad G^{(n)}[\lambda]+q^{(n,0)}[0,\lambda]$
I wanted to use ...
3
votes
2answers
83 views
Keeping specific terms in Mathematica output
Update: After solving an equation I came up with a complicated expression, is it possible to only keep some specific terms of an expression ?
As an example, if the expression is:
How can I keep only ...
1
vote
1answer
44 views
How do I force a fractional coefficient to exclude non-numeric symbols?
Short version of question: Suppose I have an expression:
expression = a+3b;
When I divide by 2, I get:
expression/2
It is ...
21
votes
2answers
444 views
Custom atomic expressions - modern tutorial
Atomic but sophisticated expressions are all around for a long time: Graph SparseArray.
More are coming witch each new release,...
1
vote
1answer
67 views
How do I extract the matrix from an density matrix equation?
I have a density matrix equation and I wish to put it in the form of a matrix.
For example, if I have:
$$\rho =Ax_{1}x_{1}+Bx_{1}x_{2}+Cx_{2}x_{1}+Dx_{2}x_{2}$$
Copy-and-paste version
...
1
vote
2answers
51 views
Finding the coefficients of a sum
Suppose I have the following expression:
p[l_] := 1 + ((1 - q) p)/q Sum[(p (2 - p))^k/q^k, {k, 0, l}]
or
$p(\ell)=1+\dfrac{(1-q)p}{q}\sum_{k=0}^{k=\ell}\dfrac{...
1
vote
0answers
57 views
how to sort an expression with descending coefficients?
I have an expression for example
psi = 0.24 FF1[0] FF2[1] FF3[-1] + 0.23 FF1[0] FF2[0] FF3[1] + 0.5 FF1[1] FF2[0] FF3[1] + 0.25 FF1[1] FF2[1] FF3[1]
I wonder how ...
2
votes
3answers
81 views
Checking if two expressions are related
Is it possible in mathematica to check if two expressions may be able to be written in terms of the other? The expressions I had in mind were of the form $$\alpha = \frac{1-x}{1-y}\,\,\,\,,\,\,\ \beta ...
6
votes
2answers
87 views
Get the intermediate steps of FullSimplify
I have this expression:
Log[i] > (i Log[i])/n + Log[n - i] - (i Log[n - i])/n
And I attempt to simplify it and get this:
...
0
votes
2answers
57 views
Require an expression to be formatted as an exponential expression
How can I require Mathematica to format an expression like
Exp[x] x^s as Exp[x + s Log[x]]?
1
vote
2answers
21 views
How to separate nested subexpressions to list?
I have an expression like this:
3*Subscript[v, 0]^3*Subscript[v, 1]^8*Subscript[v, 2]^7*Subscript[v, 3]^2
I would like to extract the exponents and put them into ...
0
votes
0answers
51 views
How to solve a Poisson's differential equation with a boundary condition at infinity?
Context: This question is relevant to the physical problem of calculating potential for a set of p-n-p junctions.
We have to solve a Poisson's differential equation for a p-n-p junction with ...
2
votes
0answers
119 views
Substitution of expressions using Groebner basis
I know this topic came up numerous times (most of the results are detailed in the comments of this link Is there a way to to substitute for symbols, simplify, and back-substitute?). However, I have ...
0
votes
2answers
69 views
Separating variables in a set of equations
I have a very large set of equations eqs with variables denoted by capital letters like PVA[2], QA[2], etc. and small letters like ica[1,2], tr[2,3] etc. And I have ...
0
votes
1answer
58 views
How to get rid of the brackets appearing in non-commutative multiply?
I am getting output as
(-T1**T2**T3)**T4**T5
How to get rid of the brackets that are appearing in the output?
I want my output as
...
1
vote
1answer
46 views
Rearranging similar terms in an equation
In a piece of code I am writing, I run into an equation of the form
...
6
votes
3answers
199 views
Taking the numerator and the denominator
Is there any way to get the Numerator and the Denominator of an expression split in the same way that Mathematica graphically represents it.
Say I have an expression:
...
0
votes
2answers
90 views
Extracting parts of an expression
I have lists with expressions like this one: {-DTMomentum2[{0, 0, 1}], DTMomentum2[{0, 0, 0}]}. DTMomentum2 is just an undefined ...
7
votes
3answers
231 views
Obtaining a matrix of complex values from associations giving the real and imaginary parts of each element?
I have a list of associations keyed by real and imaginary numbers, like so:
...
0
votes
0answers
34 views
Evaluating Fourier coefficients when Exponential terms are present
I am trying an analytical solution for a 3D Laplace equaition, and just wanted to know if I could use the symbolic calculation capabilities of Mathematica to calculate the Fourier coefficients
...
3
votes
2answers
88 views
Convert a list of lists into a list of rules
I have some trouble converting an imported list looking like this:
{{a, b}, {c, d}, {e, f}}
into a list of rules looking like this:
...
4
votes
1answer
87 views
Replacement expressions
I have the following expressions:
R[1, 1] R[2, 1] R[3, 1] R[4, 1]
sum[FF[3, ak[1] - ak[2], 1], EE[2, ak[2] - ak[3], 0], EE[2, ak[3] - ak[4], 0]]
By what ...
0
votes
1answer
73 views
How to pass an expression as list elements for a Mathematica command
I'm trying to build a generic function that will calculate sums on different iterators.
To simplify let consider:
...
1
vote
1answer
129 views
How can I use the Stirling's approximation to approximate a factorial?
I'd like to exploit Stirling's approximation during the symbolic manipulation of an expression. Essentially, I want replace Factorial[n] with ...
0
votes
0answers
21 views
Manipulating expressions containing complex exponentials and double integrals
Given that I have
Integrate[Integrate[Exp[I w (x-u+v)]f[u, v] , u], v]
$\int\left( \int e^{iw(x-u+v)} f[u, v] du\right) dv$
First, I want to first extract ...
4
votes
3answers
216 views
How is Sequence[Range[5], 3, 2] // Partition@# & parsed?
For learning purposes, I want to rewrite the following
Partition@Sequence[Range[5],3,2]
{{1,2,3},{3,4,5}}
into another one
...
