Questions tagged [expression-manipulation]
How to manipulate expressions structurally, not necessarily complying with the rules of algebra.
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Eliminate variable with partially documented Solve feature Solve[eqns,vars,elims]. Robust?
The Eliminating Variables section on Manipulating Equations and Inequalities documentation quotes an otherwise undocumented feature for Solve
...
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114
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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[[0]] = Plus;
yy
I get, as ...
- 950
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0
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260
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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 ...
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398
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Unpacking list of arguments into parameters
I have a list in the following form:
list = {{a,1,3},{b,1,3},{c,1,3}}
Now I want to apply this list as parameters for the Sum function so that I end up with the ...
- 131
3
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184
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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 ...
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3
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121
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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 ...
- 397
3
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0
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62
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How to find where in a large expression Power::infy is generated?
Consider the following expression:
...
- 7,182
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377
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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))] (* + ...*)
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3
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362
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Force expression in certain form
Is there a function in Mathematica to force an expression to be transformed into a given form. For example f[x] is a function of ...
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133
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3
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114
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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 ...
- 7,303
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2
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95
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Don't simplify integer square roots
How can I rewrite an expression like $\frac{1}{2\sqrt{3}}$ as $\frac{1}{\sqrt{12}}$?
This works in principle, but gets immediately simplified back to the original expression
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- 1,441
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52
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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
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- 201
2
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60
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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.
...
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2
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0
answers
147
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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]
...
2
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175
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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 ...
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108
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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:
...
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2
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72
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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:
...
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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, ...
- 1,278
2
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270
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ReplaceAll and derivatives
I have the following coming from a computation,
$$h_1 (u,v,w) = \frac{1}{v}\partial_v g(u,v,w)$$
and in Mathematica I have different quantities in terms of $h_1$ and its derivatives like $\...
- 203
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0
answers
109
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TrigExpand Idiosyncracies
TrigExpand[Sin[x]^2 Log[y]] returns sin^2(x) log(y), as one would expect. However, ...
- 62k
2
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1
answer
155
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Problems with 'DumpSave' and 'Save' in Mathematica 13.1 on Windows 11
My Mathematica 13.1 crashes when I try to see the result of 'Save' for some very long expressions, and produces short DumpSave files which when clicked on contain only Null.
I have a system
...
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0
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37
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Replacing an expression with pre-defined function
I am asking Mathematica to do a long calculation with functions I am defining at the beginning of the script. Because the resulting expressions are long, I want to replace them with the functions I ...
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0
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59
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Putting a polynomial into a multilinear form
Consider the polynomials in $x$ with positive-integer parameters $a,b,c$
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Evaluate coefficients of delta functions in a given expression
Suppose that I have a function of the form:
myfn[x_] = smoothfn[x] + A[x] DiracDelta[x-x0] + B[x] DiracDelta'[x-x0],
where ...
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48
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Generalizing Collect
Collect only seems to work with Times and Plus. How can we generalize ...
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28
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How to attach Upvalues to CompoundExpression?
I'm trying to make something like this work:
Evaluating
someData // Query[whatever...] /* summarizeInPrettyWay /* promptToRemoveCompoundExpression ;
should produce
...
- 342
1
vote
0
answers
37
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Replace subexpression with variable in result from Laplace transform
I'd like to clean up the result I obtained from an inverse Laplace transform:
First of all, I'd like to replace the square root expressions in the hyperbolic function arguments (part encircled in ...
- 11
1
vote
0
answers
30
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TreePosition with multiple (not just node data) conditions
Given a Tree object, TreePosition takes patterns only on the "data" of the node plus a level spec.
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1
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0
answers
79
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Can one collect with respect to two groups of variables?
Here is a toy example of what I want: given
...
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0
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108
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Same displayed expressions produce different outputs
I know EngineeringForm is a wrapper which prevents evaluation of content, but pasting chunks of other cells with an EngineeringForm number, got these two simple expressions w/ the same input ...
- 11
1
vote
0
answers
166
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How to make a function in terms of constants to inherit the attribute of being constant
I have defined two variables a and b:
SetAttributes[a, Constant];
SetAtributes[b, Constant];
I have defined a function c as ...
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1
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0
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181
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Extracting expressions from LHS of an assignment
I need to list all variables in a notebook containing several Set assignments, lhs=rhs, and equations, ...
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0
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80
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Coefficient works on $\pi$, $x$ and $x^2$, but not on $\pi ^2$
Consider
(\[Pi] + 2 \[Pi]^2 + 3 x + 4 x^2)
Executing
...
- 1,205
1
vote
0
answers
62
views
Rearranging an expression for floating point accuracy?
Does Mathematica have the feature of rearranging an expression with the goal of minimizing floating point accuracy errors? I'm asking this because I have some long expressions that really suffer when ...
- 313
1
vote
0
answers
47
views
Reading product of same ByteArrays
I am handling a huge set of data and I am trying to optimize my code. I have very large expressions to expand and simplify and I've seen that converting the expressions to ByteArrays improves a lot ...
- 1,658
1
vote
0
answers
39
views
Distinguishing function calls from multiplication when importing LaTeX via ToExpression and TeXForm
I'm trying to parse a LaTeX representation of a Desmos calculator (like this one) via Mathematica.
Desmos exposes a JSON representation of its calculators, including a LaTeX representation of ...
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1
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0
answers
48
views
How to eliminate a variable from coupled ODEs?
I found this question with an answer:
How to eliminate variables in ODE?
...
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1
vote
0
answers
69
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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 ...
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0
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96
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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 ...
- 1,648
1
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0
answers
33
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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}+...
- 141
1
vote
0
answers
63
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!
- 376
1
vote
0
answers
93
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 ...
- 111
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vote
0
answers
61
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. ...
1
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0
answers
223
views
how to sort an expression with descending coefficients?
I have an expression for example
psi = 0.24 FF1[0] FF2[1] FF3[-1] + 0.23 FF1[0] FF2[0] FF3[1] + 0.5 FF1[1] FF2[0] FF3[1] + 0.25 FF1[1] FF2[1] FF3[1]
I wonder how ...
- 1,648
1
vote
0
answers
51
views
Do replacement only on certain specific forms
If I want to replace, say, a with a1 + a2 in an expression, I can write
...
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0
answers
72
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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
...
- 11
1
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0
answers
171
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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, ...
- 1,441