Questions tagged [expression-manipulation]
How to manipulate expressions structurally, not necessarily complying with the rules of algebra.
0
votes
0answers
16 views
Manipulating expressions containing complex exponentials and double integrals
Given that I have
Integrate[Integrate[Exp[I w (x-u+v)]f[u, v] , u], v]
$\int\left( \int e^{iw(x-u+v)} f[u, v] du\right) dv$
First, I want to first extract ...
4
votes
3answers
185 views
How is Sequence[Range[5], 3, 2] // Partition@# & parsed?
For learning purposes, I want to rewrite the following
Partition@Sequence[Range[5],3,2]
{{1,2,3},{3,4,5}}
into another one
...
1
vote
2answers
48 views
Convert String in Expression to Integer
I have reviewed many string replacement Q&A but I have been unable to apply them to this case (MWE):
...
1
vote
2answers
40 views
Collect term in a distributive way
Consider
P = x (a2 b2 v^a2-1+a3 b3 v^a3-1+d1+d2-2 y)-(y-d1)(y-d2)-x
I would like to collect terms in (x,y,z) in a distributive way, that is
to get an expression ...
0
votes
0answers
11 views
Transform String to Expression [duplicate]
I have a variable postVector and another called CHKpostVector. Both are global variables.
Only the variable ...
1
vote
0answers
43 views
Do replacement only on certain specific forms
If I want to replace, say, a with a1 + a2 in an expression, I can write
...
0
votes
1answer
20 views
Extract terms containing a specific symbol from an expression
I would like to be able to extract terms that contain either a symbol or a small expression from a larger one.
Example (with a somewhat complicated function to give the idea of what I am after):
<...
3
votes
0answers
79 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 ...
1
vote
2answers
45 views
Question about replace command
I want to replace the common part in the equation by different value.
Here is my equation
...
18
votes
4answers
2k views
Cleanest way to take a[b[c]] to a[b][c]
As indicated in the title I'm looking for the fastest way to transform a[b[c]] into a[b][c], and the natural generalization to ...
0
votes
1answer
33 views
Expression replacement with variable exponents
I have an expression that consists of a large sum of variables of powers like:
X[1]^(2p) X[2]^2 + X[1]^2 X[2]^(2p) + X1[1]^(1+p) X[2]^(1+p) ...
Now I would like ...
5
votes
2answers
191 views
How to find all variables of an expression?
Is there a function that can extract a list of variables in an expression?
For example, assume we have an expression
x^2+y^3+z
This expression has variables x, y ...
4
votes
1answer
93 views
How to bring out all factors recursively except one particular term?
I want to write a function
keepOnly[expr_, keep_]
Such that
keepOnly[f[f2*g[g2*h[h2*keep, h1], g1], f1], keep]
becomes
...
0
votes
1answer
26 views
How to save numbers that stand in front of x, y, z in expression in to variables, A,B,C
I have a different plane functions in form:
Ax+By+Cz =0
I need a factors A, B, C which stand in front of variables x, y and z.
Is there any function in Mathematica to do something like this?
1
vote
1answer
41 views
Extracting parts of symbolic expressions
I've searched around and found things that could help me only in cases that are simpler than the one I had in mind. I would like to extract polynomials from expressions that schematically look like
$$...
0
votes
0answers
31 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:
...
4
votes
2answers
331 views
Drop 1st element of {#a, #b, #c} &
I pass the following to a function:
{#a, #b, #c} &
These are keys that are used in a list of associations.
There are instances where I want to pass only the ...
0
votes
0answers
43 views
How to stop evaluation of Zeta with even arguments
It could be a duplicate question. However I could not find much after a huge searching.
I have a huge expression in mathematica involving many Zetas.
I want not to evaluate the even Zetas which ...
1
vote
0answers
47 views
Selecting the 1st and then subsequent elements in an expression [closed]
I'm using a mixture of Span and Part to try and extract the arguments of a function that I need.
I'm using a function such as $...
1
vote
1answer
41 views
Factor common terms out of a sum, without changing it otherwise?
I have some expressions, that consist of rather lengthy sums such as
...
2
votes
0answers
58 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:
...
3
votes
1answer
46 views
Apply on Message resolves MessageName before applying
I want to make a Message from a List.
Message[LibraryFunction::argx, 1, 3]
...
1
vote
2answers
48 views
Define a bilinear function of strings
I have a linear combinations of strings, e.g.
combStrings = 0.1 "a" + 0.2 "b"
I want to define a function f[] which deals ...
1
vote
2answers
41 views
Move part of expression
What is the best way to take a part of an expression and put it somewhere else in the same expression? Essentially I need to combine a Extract, ...
1
vote
1answer
58 views
Simplifying a Sum of Fractions by Removing Fractions in Denominators
I have a sum of fractions of the form $x1 - \frac{(x2 + x3)}{(x4 + x5)} - \frac{(x6 + \frac{x7}{x13})}{(x8 - x9 - \frac{x10}{(x11 + x12)})}.$
How might I simplify it to remove fractions from the ...
0
votes
3answers
98 views
Replacements within a mathematica expression?
Say I have many expressions of the form $$\text{expr} = \frac{1}{AB(C+D)^n E^m}$$ where $A,B,C,D$ and $E$ are symbols and $n,m$ arbitrary powers. In order to convert between the mathematica output and ...
3
votes
1answer
37 views
1
vote
3answers
77 views
How to force an expression to be shown in terms of a specific function?
I have an integral inte1 as below:
...
2
votes
2answers
48 views
Expanding powers in an expression and Hold
Let an expression like -(1/2) + (3 x^5)/2
be given.
How can this be turned into -(1/2) + (3 x x x x x)/2?
All powers of ...
0
votes
0answers
41 views
How to use === with condition?
I have two expressions, and they are same when k is positive and x is non-zero real number. Below code gives me ...
4
votes
2answers
88 views
Expanding Log[Product[…]]
I'm trying to get the log-likelihood of a Gaussian in the form
$$
p(\textbf{x}|u,\sigma^2)=\prod_{n=1}^{N}\mathcal{N}(x_n|\mu,\sigma^2) \quad (1)
$$
$$
\ln\ p(\textbf{x}|\mu,\sigma^2)=-\frac{1}{2\...
6
votes
3answers
227 views
How can I delete a random part of an expression?
I have the expression:
Times[0.19157500241430547,Power[Plus[0.7235014213631388,k,Times[-1,Power[m,c]]],Times[g,z]]]
Also represented as:
...
5
votes
2answers
158 views
Extracting coefficients from sum
I'm having the hardest time working if I have a sum of products, with coefficients out the front, like
expr = 1 + 2 a[0] b[1] + 2 a[0] b[1] c[3] + c[6] + 5 d[3, 4]
...
3
votes
2answers
102 views
Handling long expressions
After using Expand on the result of a calculation I get a long expression which is a sum of 8654461 terms (nearly 8.7 million). ...
1
vote
3answers
62 views
Elimination of terms not containing at least one variable from a set
I have an expression with each term therein either containing at least one $n_i \in \left\{ n_1 , n_2 \dots , n_{5} \right\}$ or no $n_i$ at all. I would like to easily eliminate all the terms that ...
3
votes
2answers
135 views
Sums as rational vector dot products with a basis constants vector
I have series of values which, by visual inspection, appear to be sums of certain constants, not divisible by each other, with rational weights. I want to convert these sums to vectors of weights for ...
1
vote
0answers
51 views
Collect/Expand with D
I am new to MMA and have a basic question.
I am trying to separate the derivatives of an expression for simplification.
E.g. on doing
...
0
votes
2answers
77 views
rewriting negative powers
I often run into the problem that Mathematica refuses to simplify divergent subexpressions as part of a full expression that is manifestly finite. This only happens when a symbolic power is involved.
...
1
vote
3answers
218 views
Collect doesn't work properly
I run Want to write an expression in the form of
expr= (b rr^w+ q rr^v +...)/(c rr^n + p rr^m + d rr^s +...)
To do that, I write
...
3
votes
4answers
74 views
Splitting Piecewise with vectors to components
I have a piecewise function defined with vectors, e.g.
ab = Piecewise[{
{{a1, a2, a3}, 0 < r < 1},
{{b1, b2, b3}, 1 < r < 2}
}, {c1, c2, c3}]
The ...
6
votes
5answers
239 views
First evaluate in place all subexpressions matching pattern before substituting result
ReplaceAll[expr, {patt1:>rhs1, patt2:>rhs2, …}] works by looking for and making all possible replacements of subexpressions in ...
1
vote
1answer
49 views
Low level built-in function to transpose expression (not array) [closed]
I have an expression like this
F[G[1, b], G[3, y], G[4, y], G[5, u]]
that I would like to Transpose to obtain
...
3
votes
4answers
183 views
How to separate integers and radicals from a term?
If I have a variable such as
r = 1 + Sqrt[2] + Sqrt[13]
how can I separate that into two separate variables with the rational and irrational parts? i.e.
...
0
votes
1answer
24 views
Keeping terms separate without combining it especially with multiplied random numbers
Suppose I have an expression where random numbers in exponentials are multiplied and this expression will keep on iterating such that more of such terms will occur. But I need to keep those terms as ...
5
votes
2answers
133 views
How to mark leaves of polynomial based on its position in tree
I've been struggling with this for a few days, and so I thought I might ask this here. Part of the problem lies in the fact that I do not even know the mathematical solution, which runs the risk of ...
1
vote
0answers
110 views
Split expression into nested list of summands, times and dot products
In order to avoid the XY Problem we might have encountered in another question I asked, here I ask a new question with full context:
I want to get a list representation of an expanded expression, ...
0
votes
0answers
31 views
Assume Symbolic Elements as Scalars in Distribute
So yesterday I asked about TensorExpand but it turns out that it is way too slow for my needs. I want Mathematica to know that my symbolic variables are scalars, so I don't have the parentheses in my ...
1
vote
1answer
32 views
Assume symbolic elements as reals in TensorExpand
Let's assume that a, b are complex variables, and A[t],B[u], C[t,u] are matrices.
...
1
vote
1answer
40 views
How to force Refine to use a specific form
I have an assumption relating three variables and Simplify (and all functions that use assumptions) seem to take preference on one of these variables. For example:
...
2
votes
0answers
47 views
How does one generically expand the argument of a gamma function? [closed]
I have expressions of the form
Gamma[2 (56 + k)]
which I would like to convert to
Gamma[112 + 2 k]
But
...
