Questions tagged [expression-manipulation]

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

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63 views

How to test if $ⅈ$ is in an expression?

From this answer https://mathematica.stackexchange.com/a/9773/68791 and according to the documentation: FreeQ[list,form] test whether form occurs nowhere in ...
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52 views

General rule to rewrite function and argument into a new symbol

I am trying to convert Mathematica output into equations I can plug into C. I am presently trying to convert expressions of the form Derivative[1,0,0][f][t,x,y] ...
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1answer
63 views

Collect integer and non-integer powers at the same time

Imagine we have an expression that contains both integer ($y$, $y^3$, $y^8$ etc.) and non-integer powers ($y^{1+\alpha}$, $y^{2\,\alpha}$, $y^{2+3\,\alpha}$) of the variable $y$, where $\alpha\in\...
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2answers
110 views

Expand in series an equation of two variables

I am sorry if this has been asked, I don't really know how to formulate the search to find it. We have some system of equations (that are equal to zero), for example (not sure how to enter ...
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How can I force the output of a computation to be as compact as possible, yet complete, by using functions?

I am computing some derivatives in Wolfram Mathematica 11.3. The functions that I have to differentiate (with respect to the state variables) are the equations of motion of a rocket in the atmosphere. ...
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Evaluating meta expressions of (partial) derivatives

I have created some meta expressions for many derivative calculations such as ...
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1answer
112 views

How to make a function linear

I have a linear function, say f, and an expression like f[3x^2 - 8 a y^2 + 4 z b] where I know that ...
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1answer
43 views

How can I calculate the union of a tagged set? [closed]

I want to calculate: Union[envelope[1], envelope[2], envelope[3], envelope[4], envelope[5], envelope[6], envelope[7], envelope[8], envelope[9], envelope[10]] ...
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2answers
76 views

Suppress arguments in output for pretty print

I would like to define a rule that suppress any arguments of a function for visibility. I tried: rule = f_[x__] -> f While this works well with individual ...
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1answer
43 views

Matrix multiplication of function

Suppose I had a 2-by-2 matrix with each entry a function, e.g., {{#1&,#2&},{#1 + #2 &, -#1 + #2 &}} and a vector of functions, e.g.,...
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1answer
46 views

Gradient of function with arbitrary number of variables

This link answers the question on how to express the derivative of a function with an arbitrary number of variables. However, what if I wanted the gradient? More specifically, if ...
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1answer
100 views

n derivatives on a function of n variables

I want to derive an expression with respect to each variable of a function $f: \mathbb R^n \rightarrow \mathbb R$. More precisely: $\left(\prod_{i=1}^n\frac{\partial}{\partial_{x_i}}\right) g(f(x_1,...
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1answer
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Prevent argument substitution in held expression when injecting into unevaluated code

I want to write a custom sow/reap pair to wrap any piece of code in sow[code] and call reap ...
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1answer
38 views

Expression with Boole

Let us have an expression for example, this: 2 (-1 + p) (3 - 4 p + 2 p^2) Boole[\[FormalX] == 1] - 9 (1 - 2 p + p^2) Boole[\[FormalX] == 2] ... For the whole ...
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1answer
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Extract variables from sum of unevaluted functions

I have sums of the form sum = a f[1,1,0] + b f[1,2,0] + c f[1,2,1] + ... It is always linear in f[a,b,c]. I would like a ...
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1answer
72 views

Output of `Subsuperscript` in TeXForm?

TeXForm can be used to convert Mathematica expressions directly to LaTeX. However, this function fails on an expression that has a sub- and a super-script: ...
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1answer
43 views

How to generate a list (or even a sequence or a string) containing {x[1]==0&&x[2]==0&&…&&x[10]==0?

I need to solve a bunch of systems of n equations in n unknowns where n varies. I can do ...
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1answer
77 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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1answer
172 views

Conflict with hidden names

The following code hangs Mathematica 12.0.0: ...
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1answer
105 views

Strange behavior of `Apart`

Here is a piece of sad comedy based on some Apart behavior. Is there a way to make Apart do the expected step? Consider a very ...
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0answers
71 views

Is there a good reason why `Slot[]` is not an atomic expression?

Here's a good reason why I think it should be, Map[ If[AtomQ@#, #->"is an atom", #->"not an atom"]& , {"hello",Range@3, # &} , {-1} ] ...
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3answers
159 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
42 views

Narrowing the range of an interpolating function while keeping integral the same?

Consider an interpolating function derived from some data, e.g. ...
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1answer
94 views

Expandable summary view for a large expression

I need a convenient interface to interactively explore very large expressions. I am aware of Short and Shallow, and appreciate ...
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Expressing Numbers with Rational Denominators (Surd Form) [duplicate]

Is there a command which expresses given real numbers in surd form (when possible)? That is, a form where any rooted terms are placed in the numerator, and the denominator is rational. Here are some ...
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1answer
42 views

Replace sub-expressions matching a pattern unless located under specific heads

Suppose I have some rule, e.g. Re[x_] :> (x + Conjugate[x])/2. I want to apply it to all matching sub-expressions in some expression, excluding any sub-...
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1answer
47 views

How the terms are arranged in `CoefficientList` command?

I have an expression containing various orders (powers) of F[r]. Using CoefficientList, the output is a blue box which is ...
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2answers
73 views

Exclude the terms from determinant

i have a long determinant expression such as delta=8+2a+3b+4c+50a^2+2a^3+70b^2+80a*b+20(a^2)b+5(e^x)+a*b(e^x)+....+3e^(-x)+.. I want to exclude the expression ...
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0answers
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Wrong derivative for a function that I try to define without explicitly giving number of variables

What I actually want is to define functions depending on the number of variables which will be specified during some computation. My (probably wrong) attempt is ...
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3answers
319 views

Evaluated vs. unevaluated Association

This question might have a remote connection to my older question, it is also about sameness of expressions and subtle differences observable only in certain forms. I encountered this strange ...
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2answers
122 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 ...
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0answers
59 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 ...
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1answer
48 views

Generating examples by applying conditions to symbolic expressions

For example, Given a list of symbolic expressions: ...
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0answers
32 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 ...
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0answers
59 views

How to show the sign of an algebraic expression?

I defined a long expression ...
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1answer
580 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. ...
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2answers
79 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 ...
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3answers
115 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. ...
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1answer
40 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 ...
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2answers
265 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
34 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 ...
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3answers
253 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: ...
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1answer
92 views

Need help in understanding what Extract does

Can anyone explain two examples from the Mathematica Documentation Center reference page on Extract? One is: ...
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3answers
102 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
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1answer
48 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 ...
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3answers
37 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 ...
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1answer
65 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.....
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2answers
56 views

Groupings over non-atomic elements

I use groupings as below: Join[ Groupings[IntegerPartitions[3], {A -> {2, Orderless}, B -> {2, Orderless}}], {x}] Which generates: ...
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1answer
27 views

Groupings: orderless version?

Consider the following groupings code: Groupings[IntegerPartitions[3], {A -> 2, B -> 2}] This generates: ...
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3answers
108 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 ...

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