# Questions tagged [expression-manipulation]

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

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### Calculate density of states for 1D system

The density of states for a 1D system can be written as: $D\left(\omega\right)=\frac{L}{\pi}\frac{1}{d\omega\left(k\right)/dk}$ I have some expressions for $\omega\left(k\right)$: ...
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### Substituting values from an association thread into a table of expressions

I have asked a question here. Yet I am trying to do the same procedure with AssociationThread Suppose I have the following function which is a normal distribution: <...
51 views

### Substituting elements of lists into an expression

Suppose I have the following lists, as = {1, 2, 3, 4}; bs = {10, 20, 30, 40}; and the following expression: ...
53 views

### Crown a list of two sublists with ErrorBar without losing list structure

I have a list with two sublists of numbers, e.g. Sigmaf = {{1,2,3},{3,4,5}}; ... and I would like to crown each number with ...
82 views

### Split Expression Into Constant And Non-Constant Summands

I have a partially t-dependent matrix which I want to split into its t-dependent and its t-...
191 views

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### Testing expressions with === (SameQ) between original expression and after Factor[], Expand[] and FullSimplify[] [closed]

a=16x^4 y^5 (81-z^4)-54xy^2 (81-z^4) Out[30]= -54 xy^2 (81-z^4)+16 x^4 y^5 (81-z^4) b=Factor[a] Out[31]= 2 (27 xy^2-8 x^...
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### How do I apply complicated algebraic/trigonometric manipulations to nested expressions?

Consider the expression $$a\sin(x)-a\sin\left(\frac{x}{a}\left(a+\frac{ay}{x}\right)\right) \label{a}\tag{1}$$ which can be rewritten as $$\sin(x)-\sin\left(x+y\right) \label{b} \tag{2}$$ and ...
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### How do I build a position index of a general held expression to arbitrary depth?

I have an expression which I would like to make a position index of, which for sake of argument will be this: expr = f[q + g[x, y, z]]; Since it's not a list, ...
48 views

### Extracting argument of a specific functions in a large expression

I have a large expression, for example Cos[x]Sin[y]Sqrt[1+z]/(1+x^2)-1/(1+y) I wish to extract the argument inside Sqrt ...
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### Finding a selected expression

How can I find all expressions matching the one I am selecting? This features exists in Matlab and is quite helpful: Just trying to make my debugging easier. Thanks!
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### How to do an arbitrary expression growth in Mathematica?

I want to write a function that can be used to grow an expression from a seed or another existing expression based on part specification. ...
620 views

### Split expression into list of terms

I'm looking for a nice way to split an expression into a list of the terms (i.e. the addends). The desired behavior in: ...
45 views

### Canceling factors from numerator and denominator with complex number

I have the following expression: $\text{expr} = i \frac{\sqrt{a-b}}{\sqrt{b-a}}x$. Clearly simplifying expression gives $\text{expr}=x$ by cancelling the numerator and denominator. However, I am not ...
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### Any differences between Activate[…] vs ReplaceAll[…,Inactive[f_]-f>]?

I can activate an expression with Inactive objects such as expr = Inactive[f][Inactive[f][x], y] + Inactive[f] by applying <...
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### Manipulate MeshRegion as normal Mathematica expression

A MeshRegion seems to function quite differently from any other Mathematica expression. One cannot take a Part of it. Nor can I ...
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### How can I show that the equation holds?

Suppose we have the following data: $r=\frac{vk}{h^2}$ $u[i,j]$ is a function of two variables with $i,j$ integers. $\frac{u[i,j+1]-u[i,j]}{k}=v\frac{u[i+1,j]-2u[i,j]+u[i-1,j]}{h^2}$ Then I would ...
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### Assert no unevaluated function applications

Background Suppose I have begun a fresh kernel session, and I have defined the following function alone: F[x_, y_] := x + y; One expected use of ...
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### Making substitution to an expressions with a list of numerical data [closed]

Suppose I have an expression similar to this: y=23.23*(h[x]^2)*(D[h[x],x])*(D[h[x],{x,3}])/(13.2+Cos[0.245x]) The actual expression is a lot more complicated, but ...
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### Select variable and its derivatives

A simple question: I have this equation: ...
341 views

### isolating a specific variable to one side in an equation

I am trying to do a simple operation of manipulating an equation of multiple variables (say, $x,y,z$), so that I can get one of the these variables on the LHS and everything else on the RHS. It should ...
88 views

### Remove imaginary part from expression on an interval

Let us have a expression: ...
1k views

### Which operation combines {f,g,h,…} and y[u,v,w,…] to get y[f[u],g[v],h[w],…]?

I have a list of functions myFuncs = {f,g,h} which I'd like to map over an expression expr = y[u,v,w] to obtain ...
332 views

### How to make arbitrary transpositions of associations and datasets

Is there a general Transpose for Dataset/Association that will transpose arbitrary levels, ...
107 views

### ReplaceList doesn't apply rules down to subparts

Somewhat related to a previous question, I'm experimenting with ReplaceList to get the list of all possible transformations we can obtain by applying a rule to an expression. But I don't manage to ...
68 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 ...
59 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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### 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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### 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 ...
58 views

### 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. ...
221 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 ...
46 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]] ...