# Questions tagged [expression-manipulation]

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

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104 views

### Why does the kernel quit if I want to use minus a sum that I converted from a list?

Using Mathematica 11 when I define a list yy = {x*43, 32*y}; and then convert it to a sum yy[] = Plus; yy I get, as ...
231 views

### Why doesn't Log[Gamma[]] simplify to LogGamma[] where it could?

I have been playing with various equations involving amount of permutations in relatively large sets. Easiest way to look at these is something like Log[10, bignumber!] . Often expressions, even ...
87 views

### Select certain term containing some patterns and confusing pattern Alternatives in FreeQ

I am considering a function termsContain[func_,list_] which select in an expression func the terms containing the ones in the ...
54 views

### How to find where in a large expression Power::infy is generated?

Consider the following expression: ...
265 views

### Bringing rational functions to canonical form

I have a complicated expression, which among other things has stuff like functions of rational functions: expr = f[x/(-x^2 + y)] + f[-(x/(x^2 - y))] (* + ...*) ...
125 views

### Check an Option without Evaluation

Consider the following: ...
106 views

### How to combine DifferenceRoot objects for odd and even-indexed terms

I'm trying to analyze a certain infinite sequence $S$, indexed by positive integers starting from $1$. It can be split into two subsequences: $S^{odd}$ by removing all even-indexed elements and ...
99 views

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### Define quaternions by properties instead of coordinates

I'd like to manipulate an expression of quaternions and only use the following properties ...
27 views

### Computations with OptimizedExpressions without completely expanding them

I have to manipulate huge expressions that are rational functions of many (∼30) variables with integer coefficients. Storing them just as a ratio of two polynomials would be impractical. But they can ...
54 views

### 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. ...
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] ...
129 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 ...
63 views

### Generating a list of 4-digit integers by simulating four dice being thrown eight times

I simulate throwing four dice and merge their values together to form a 4-digit number. This is done eight times and I want to get a list like this one: ...
59 views

### Create Association from Expression

I have a set of algebraic expressions of a certain form, and I would like to make them into Associations in a specified way. My expressions are formed of two heads, ...
231 views

### Derivative of vector dot product with respect to a vector

I have the expression: Transpose[gvecI, {2, 1}].x (m + m) gvecI and x are [3x1] ...
98 views

### TrigExpand Idiosyncracies

TrigExpand[Sin[x]^2 Log[y]] returns sin^2(x) log(y), as one would expect. However, ...
41 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 ...
49 views

### Fast way to apply permutations in large list?

I have one Polynomial in the form of FF[x1,x2,x3,x4,x5,x6,x7,x8], where xi pick numbers from ...
44 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.
28 views

189 views

### How to invert an Elliptic function where the elliptic nome is a function of an independent variable?

I have a Jacobian elliptic function as a function of two independent variables $x$ and $y$. The elliptic parameter $m=m(y)$, $0 \leq m \leq 1$, is also a function of the variable $y$, and thus the ...
86 views

### How can PowerExpand be made to evaluate the ArcTan form that takes two arguments?

Consider c = Cos[phi]; s = Sin[phi]; ArcTan[c, s] // PowerExpand ArcTan[s/c] // PowerExpand which yields ...
50 views

### Factoring rationals from equation based on digit complexity?

Consider an equation of the following type: ( poly = (3 x)/35 + (6 y)/7 ) == 0 If we apply the command Factor to this ...
60 views

### Matching Root[…] objects with patterns, unexpected hidden argument

I needed to write patterns that could distinguish between arbitrary-function and polynomial forms of Root objects, for example, ...
32 views

### 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 $\omega\left(k\right)$: ...
54 views

### check if one expression can be transformed into another

My question is how to use Mathematica to check if one expression can be transformed into another: Example 1: $ax^2+bx+c$ into $K\cdot(x+\alpha)^2+\beta$, and then show me $K(a,b,c)$ and so on. ...
32 views

### Expanding complex expression and replacing variables in the result

When I'm finished expanding my expression I would like the result to be expressed again in terms of the original variables (like α, S1, T1, T2). I've tried replace, ...
38 views

### Rearranging expressions by DragAndDrop

I see that the DragAndDrop option for editing is not supported anymore. However, I think this could be a really useful feature, for instance to rearrange the terms of an expression in the form we ...
18 views

### Comparing fractions by using partial fractions or a specific factorisation?

Trying to reproduce the results of a paper I had to solve a difficult integral. I obtain: \begin{equation} A=-N\left ( \epsilon r+\log(1+r) +\frac{rx^2(1-r\tau + \tau r^2 (\tau +1))}{1+r}+\frac{ry^2(-...
20 views

### Evaluating meta expressions of (partial) derivatives

I have created some meta expressions for many derivative calculations such as ...
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 ...
42 views

### 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 ...
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 ...
59 views

### How to show the sign of an algebraic expression?

I defined a long expression ...
66 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 ...
42 views

### Manipulating Equations: Substracting two equations

I was wondering why I fail to substract two equations using thread, while it works properly, as described here for additions. Example: Let a system of equations be given: ...
46 views

### How to use === with condition?

I have two expressions, and they are same when k is positive and x is non-zero real number. Below code gives me ...
### Proving $d(dx)=d^2x$
Is it possible to carry out the following differential in Mathematica? $$d(dx) = d^2x$$ I tried to write: Dt[1*Dt[x]] the result is: ...