Questions tagged [expression-manipulation]

How to manipulate expressions structurally, not necessarily complying with the rules of algebra.

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34 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 ...
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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, ...
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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 ...
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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? ...
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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 $a_i b_jc_kd_l$, ...
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2answers
34 views

How do I integrate the result of a DSolve operation?

I've got the following result from evaluating a DSolve problem: ...
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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@ ...
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1answer
117 views

Transform rational equations to polynomial equations

I have a list of rational equations and I would like to convert it to a list of polynomial equations. I know that none of the variables and none of the denominators could ever be 0. So far I have ...
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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 ...
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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 ...
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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 ...
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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: ...
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3answers
485 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: ...
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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 ...
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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 ...
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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 ...
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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 ...
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1answer
52 views

Optimizing an equation - show the length of an equation, including operators

A simple, but I think useful question to know the answer for. How can I quickly count the length in my equation, including +,-, and so on? For example, $x^2+1$ has a length of 4.
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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: <...
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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 ...
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2answers
1k views

Adapting CoefficientList (and the related functions) to work with Laurent polynomials

Is there a slick way to make CoefficientList (and the other similar functions, CoefficientRules etc.) work for Laurent ...
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1answer
102 views

Extracting a product of factors from an expression in unevaluated form

Suppose I have an expression like so: $\qquad {\rm expr}=2\,i\,{\rm Gamma}(4)\,\pi\, 9.93 f(x)\,g(y) \frac{h(x, 4y)^3}{11 q}$ What is best (most succinct) way to extract out only the product of ...
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3answers
166 views

How to extract the argument from an in-built function

I would like to extract the argument from : DiracDelta[-10 + x + ξ]
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1answer
75 views

Factorization of multivariable polynomial

I have a multivariable polynomial, for instance: $P=yx+2^4xy+3+5^2xz+3^4zx $ I would like to do the following: extract those terms that only have $z$ extract terms that only have $y$ express my ...
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1answer
119 views

Expand terms of series in denominator

I have equation: $a+bx+cx^2+dx^3= \dfrac{1}{f+gx+hx^2+ix^3} \dfrac{\partial}{\partial r}(ax+bx^2+cx^3+dx^4) +\dfrac{1}{(f+gx+hx^2+ix^3)^2} \dfrac{\partial^2}{\partial r^2}(ax^2+bx^3+cx^4+dx^5)$ ...
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1answer
706 views

How to convert an image to a compressed string representation equivalent to one copied to clipboard by `CopyToClipboard[image]`?

In my recent question I asked How to embed an image into a string? The suggested solution was ...
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2answers
58 views

Collect terms in inverse powers of three variables

I have the following expression ...
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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 ...
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3answers
233 views

How to replace $x$ and $x^2$ with different value?

I have an expression now expr = x + x^2 what I want to do is to replace $x$ with $k\times p$ , and $x^2$ with $[k\times p + k\times(k - 1)\times p^2]$. The ...
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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 ...
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1answer
204 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 ...
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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 ...
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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 ...
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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 ...
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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) == ...
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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 ...
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0answers
115 views
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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'...
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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 ...
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0answers
41 views

How to eliminate a variable from coupled ODEs?

I found this question with an answer: How to eliminate variables in ODE? ...
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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. ...
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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
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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
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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: ...
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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 ...
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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
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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 ...
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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 ...
95
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4answers
5k views

Replacement inside held expression

I wish to make a replacement inside a held expression: f[x_Real] := x^2; Hold[{2., 3.}] /. n_Real :> f[n] The desired output is ...
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1answer
61 views

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