Questions tagged [expression-manipulation]
How to manipulate expressions structurally, not necessarily complying with the rules of algebra.
641
questions
0
votes
0answers
39 views
Exponential matrix, run during infinit amount of time
Context: I want to apply an exponential matrix on a vector. The size of the matrix (which then I apply the MatrixExp on) is size of 50x50, and not diagonal. For reason I don't know, Mathematica take a ...
5
votes
1answer
92 views
Extracting n-th part of an expression without any evaluation
Is it possible to extract n-th part of an expression as a string, without any evaluation?
For example,
...
1
vote
0answers
27 views
Rearranging an expression for floating point accuracy?
Does Mathematica have the feature of rearranging an expression with the goal of minimizing floating point accuracy errors? I'm asking this because I have some long expressions that really suffer when ...
0
votes
1answer
40 views
How to filter out “relevant” information from expression
I have an expression of the form
op = a3 b2 c1 d0 - a2 b3 c1 d0 - a3 b1 c2 d0 + a1 b3 c2 d0 + a2 b1 c3 d0 +...
that is, each term is of the form $a_i b_jc_kd_l$, ...
1
vote
2answers
34 views
How do I integrate the result of a DSolve operation?
I've got the following result from evaluating a DSolve problem:
...
2
votes
2answers
144 views
I want to turn an equality statement into a function
I've got a statement (condition?) that I want to integrate.
r'[t] == (2*(c + A*t)*(1 + z))/(2 + z)
What's the best way to integrate just the RHS of this equality? ...
2
votes
2answers
102 views
Map a function at one “part” of each term in a multivariate polynomial
I have polynomials in several variables x[i] and y[j], and I am using First@SymmetricReduce@ ...
1
vote
0answers
40 views
Unpacking list of arguments into parameters
I have a list in the following form:
list = {{a,1,3},{b,1,3},{c,1,3}}
Now I want to apply this list as parameters for the Sum function so that I end up with the ...
0
votes
0answers
38 views
How can I use a replacement rule as part of a simplification?
I am using Mathematica to symbolically calculate the likelihood for a simple linear regression model. As part of this I want to substitute
...
1
vote
1answer
38 views
How to change numbers in variables defined with a loop?
I am trying to change the number which is part of the variable name with a loop.
What I want to changue is the following:
...
1
vote
1answer
60 views
Writing mathematical expression in a file
I am trying to write a mathematical expression as variable = expression in the output file.
The current method that I am doing is through ...
3
votes
1answer
46 views
Rationalizing only specific terms in an expression
How can I change an expression like
A = (-1. a)/(x + y) - (2.1 b)/(x + y) + 4.1 + 2. x + (3. r s)/(x + y)
so that -1. a becomes ...
4
votes
2answers
1k views
Write x^3 as x*x*x
I use mathematica compute functions I need for some external coding. However I can't use terms like x^2+y^3 since my programming language needs this term written as ...
0
votes
2answers
50 views
Replace small expressions in larger expressions?
How can I replace small expressions in larger expressions?
Simple example
Replace[a^2 + b^2 + 2*a*b + x, (a + b)^2 -> c]
I want to get ...
2
votes
1answer
36 views
Passing an expression to the Plot Function does not Work
Solving a differential equation I found that its solution was analytic, and I stored it as an expression from the default rule output of the DSolve[] function:
<...
6
votes
1answer
70 views
Compile - Optimization of function calls - does it matter?
I was surprised to see that, in the results of CompilePrint for a function made with Compile, calls to ...
1
vote
1answer
69 views
Exploring curl of a gradient of a scalar function
Suppose I want to explore $\nabla \times \nabla V$ where $V$ is some scalar function. It basically results in a zero. But I would only know why if I solve it on paper. I wanted to use Mathematica for ...
1
vote
2answers
58 views
0
votes
0answers
33 views
Simplify the coefficient of an expression after calling Collect
I have an expression for which I have run Collect to get the expression in terms of a few variables. I now want to run Collect ...
-1
votes
1answer
61 views
Combining multiple graphs in one photo without consulting external programs [closed]
I want to add many plots from Mathematica into one picture and export as a PDF. Usually I select the plot and copy it as an image to Word, however the image reduces the accuracy of some plots.
How can ...
1
vote
0answers
42 views
Reading product of same ByteArrays
I am handling a huge set of data and I am trying to optimize my code. I have very large expressions to expand and simplify and I've seen that converting the expressions to ByteArrays improves a lot ...
4
votes
1answer
91 views
Force results to be displayed in a way often seen in traditional math [closed]
I want to get my output in the form that I would write by hand. I have tried with TraditionalForm, but it did not work.
I've looked at several answers in this SE ...
1
vote
1answer
205 views
Desktop vs. Cloud option, home plan vs. basic plan: syntax differences
I do not understand why the following simple expression is accepted using a browser (cloud option), but is not accepted using the installed software (desktop option) with the plan basic of Wolfram ...
0
votes
1answer
49 views
Find n-th derivative of the function, display it and then evaluate it at a point of choice
What would be the correct syntax to find the order derivative "$n$" in MMA, and to be able to evaluate it in a certain point.
We ask for an example ;
Find the order derivative 2 and evaluate ...
0
votes
1answer
83 views
Mathematica refuses to distribute a scalar through parentheses
I’m working on a problem involving Kelvin-Helmholtz instability and I’m trying to perform the linearization on Mathematica. For some reason when I get to my first order equation (ε × stuff + O(ε²) == ...
1
vote
0answers
27 views
Distinguishing function calls from multiplication when importing LaTeX via ToExpression and TeXForm
I'm trying to parse a LaTeX representation of a Desmos calculator (like this one) via Mathematica.
Desmos exposes a JSON representation of its calculators, including a LaTeX representation of ...
1
vote
0answers
115 views
What is the difference between NSolve and N[Solve] [closed]
N[Solve]
NSolve
I am getting different results everytime I use these commands.
2
votes
2answers
77 views
How can I get output from Reduce assigned to a variable? [closed]
I use Reduce to solve an 3rd order equation, and the output is given as the OR'd combination the solution variable. Normally, I can do a replacement to assign the value to a variable, but that doesn'...
0
votes
0answers
50 views
Any way to automate solving problems where the answer from one question is used in the next?
I am a total Mathematica beginner. I just want to use it to do some calculations, and the reason it is so interesting and attractive to me as an engineering student is that it allows me to write maths ...
1
vote
0answers
41 views
How to eliminate a variable from coupled ODEs?
I found this question with an answer:
How to eliminate variables in ODE?
...
3
votes
3answers
60 views
Computing the sum of the first row of a matrix
I wish to compute for the sum of the reciprocals of the first row of the distance matrix of a particular circulant graph. My code is as follows for the ordinary sum of the first row.
...
1
vote
1answer
130 views
Quantum bra and ket notations
Is there a way to define the above quantum expression in Mathematica. I am using an add on package in this link. http://homepage.cem.itesm.mx/lgomez/quantum/
What I have tried is:
...
7
votes
2answers
137 views
Better way to rename arguments to a functional form so that duplicate arguments are sequentially enumerated
I need to modify expressions that such as f[w, w, a, y, x, a, x, a] into f[w1, w2, a1, y, x1, a2, x2, a3].
In short, I have ...
2
votes
3answers
142 views
Simplifying expressions containing binary variables
Consider an expression with two binary variables, $a,b\in\left\{ 0,1\right\} $, given by $F=(1-a-b)^{3}(1-b)$, with truth table:
...
5
votes
4answers
195 views
Equivalent of select/remove for Mathematica?
What is the Mathematica equivalent of Maple's select/remove?
To quote Maple:
A typical application that uses select and remove ...
0
votes
0answers
47 views
Shorten a sum of many terms by introducing a rule for scalar product and Kronecker deltas and using repeated replacements
There is a sum of many terms that I would like to simplify by introducing a notation for scalar product of two vectors. Each term is a product of constants and of several components of 3D vectors: <...
2
votes
2answers
94 views
How to Simplify expression efficiently inside Power
How can I simplify trivial expressions under the Power?
Here is one example:
(z2p-z2p z3)^-ϵ
...
2
votes
1answer
61 views
How to extract terms from equation, and then set each of them to 0?
I have a long equation, namely,
...
6
votes
1answer
69 views
Collecting common powers of terms
How to collect the common powers appearing in the following function using MATHEMATICA, such that if I input
(4 m^6)/((m - n)^2 (m + n)^4 (2m+n)^4)
then the ...
1
vote
2answers
75 views
How to sort out/ extract positive and negative powers as list?
I have the following expression
expr = x1^d1 * x2^d2 * x3^d3;
where d1,d2,d3 can contain negative values/expression i.e. in ...
2
votes
3answers
129 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} ...
2
votes
1answer
59 views
How to get the result in terms of a previously defined expression?
Say I have a vector
X[n_] := Table[Subscript[x, i], {i, 1, n}]
and a matrix of connections:
...
0
votes
0answers
28 views
Why are these expressions with shifted delta functions not equal?
I have the following equation
Exp[a-t]*DiracDelta[t-a] == DiracDelta[t-a]
which cannot be evaluated. However, if I plug in 0 for a:
...
1
vote
2answers
39 views
Substitute an expression iteratively
I have defined this function
replaceIteratively[expr_, x_, list_] := Module[{n = 0}, expr /. x :> (n++; list[[n]])]
which does the following job
...
0
votes
1answer
137 views
How can I obtain the matrices of coefficients of quadratic form?
I'm trying to find the matrices of coefficients of a quadratic form:
...
5
votes
1answer
132 views
How can I emulate Orderless attribute?
Suppose I want an expression to automatically sort its arguments. This can be done via
SetAttributes[f, Orderless]
f[3, 2, 1]
(*output is f[1, 2, 3]*)
Just as an ...
1
vote
0answers
42 views
Finding the domain in which a function is analytic with no imaginary part
I was wondering if it is easy to see if a given expression evaluates to a real number in a given domain? Let e.g. f(x,y,z) be some function depending on three ...
0
votes
1answer
97 views
How to check if an expression is real in some domain
I was wondering if it is easy to see if a given expression evaluates to a real number in a given domain? Let $f(x,y,z)$ be some function depending on three variables $x,y,z$. I would like to know if $...
2
votes
0answers
46 views
Define quaternions by properties instead of coordinates
I'd like to manipulate an expression of quaternions and only use the following properties
...
2
votes
1answer
86 views
Converting an equation to the form $ax+by=c$
I have a linear equation that comes as a result of applying orthogonality on a non-homogeneous boundary condition with two unknowns $C_1$ and $C_2$. Can someone help me to express this equation in the ...
