Questions tagged [expression-manipulation]
How to manipulate expressions structurally, not necessarily complying with the rules of algebra.
596
questions
2
votes
1answer
58 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 ...
1
vote
0answers
35 views
Simplifying the final coefficient expression of a PDE solution
I have been trying to solve a boundary value problem analytically which involves a three-dimensional temperature Laplacian over a parallelepiped. In the final step of my solution, using the two non-...
0
votes
0answers
29 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 $\omega\left(k\right)$:
...
1
vote
2answers
40 views
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:
<...
5
votes
1answer
45 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:
...
2
votes
1answer
43 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 ...
5
votes
1answer
64 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-...
5
votes
2answers
154 views
Replace a randomly chosen part of an expression
Given an arbitrary Mathematica expression, how can I choose a random part of the expression and replace it with another symbol of my choosing?
For example, given $a x^3 +2y\cos(x)- \tanh(x^{y+3})/(x^...
1
vote
1answer
74 views
Fixed Point Iteration - Finding Iteration Functions
When we use Solve, it attempts to solve the system for the variables, for example
Solve[x^3 + 4 x^2 - 10 == 0, x]
If we want to use Fixed Point Iteration to ...
2
votes
1answer
51 views
Extracting coefficients from a sum of exponential functions
I'm dealing with a sum of exponential functions with different exponents
...
2
votes
1answer
29 views
Problem with recursive relations
Continuing the topic of my previous questions (link1 and link2), let me ask one more question.
I have problems with the following code:
...
0
votes
0answers
53 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.
...
2
votes
1answer
53 views
Replace a family of coefficients by a function in a sum
I would like to do something very simple, i.e. replace the coefficients in a sum by a function:
c[1] + c[2] + c[3] /. {c[s] -> (s + 1)/(2 (2 s + 1))}
...
2
votes
2answers
60 views
Symbolic nest expressions
I'm trying to understand how to use symbolic expressions as arguments. The following example represents my problem:
...
0
votes
1answer
31 views
using pattern matching to separate coefficients and functions
I want to find out the coefficients and functions from an expression and possibly save them in separate files with same order.
I have the following toy example:
...
2
votes
2answers
76 views
Collect with linear combinations
Is there a way to collect coefficients on specific linear combinations of variables? Consider the example below:
...
0
votes
0answers
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 Ī±, S1, T1, T2). I've tried replace, ...
2
votes
0answers
27 views
Computations with OptimizedExpressions without completely expanding them
I have to manipulate huge expressions that are rational functions of many (ā¼30) variables with integer coefficients. Storing them just as a ratio of two polynomials would be impractical. But they can ...
0
votes
0answers
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 ...
0
votes
1answer
29 views
Applying function to both coefficients and variables in Collect
I am dealing with expressions schematically of the form
expr = c[1] G[1] + c[3,8] G[3,8] + ... + c[3] G[1] + ...
where the Gs are fixed objects, and the cs some ...
1
vote
0answers
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 ...
1
vote
1answer
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.
2
votes
3answers
70 views
How to hold the expression when using ToExpression with TeXForm
I know
{1, 1} // Apply[Defer@*Plus]
can return
1+1
But if I want hold the form from TeXForm,what should I do?
...
1
vote
0answers
28 views
Lexicographical Search and Conjugate
I bid you a good day.
I want Mathematica to plug this assumed solution into the left hand side of a differential equation. Then collect terms of powers of $\alpha$.
$\psi (x,y)=\alpha f_1(y)e^{i x}+...
0
votes
1answer
24 views
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^...
2
votes
1answer
61 views
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 ...
4
votes
1answer
57 views
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, ...
1
vote
1answer
34 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 ...
1
vote
0answers
55 views
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!
2
votes
0answers
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.
...
6
votes
3answers
227 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:
...
0
votes
0answers
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(-...
1
vote
0answers
38 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 ...
7
votes
1answer
72 views
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 <...
0
votes
1answer
55 views
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 ...
1
vote
1answer
65 views
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 ...
6
votes
2answers
85 views
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 ...
0
votes
1answer
32 views
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 ...
2
votes
3answers
76 views
3
votes
3answers
130 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 ...
1
vote
3answers
60 views
16
votes
7answers
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 ...
13
votes
3answers
291 views
How to make arbitrary transpositions of associations and datasets
Is there a general Transpose for Dataset/Association that will transpose arbitrary levels, ...
4
votes
4answers
97 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 ...
1
vote
1answer
61 views
How to test if $ā $ 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 ...
2
votes
0answers
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]
...
0
votes
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\...
0
votes
2answers
109 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 ...
1
vote
0answers
52 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. ...
0
votes
0answers
20 views
Evaluating meta expressions of (partial) derivatives
I have created some meta expressions for many derivative calculations such as
...
