Questions tagged [replacement]
The replacement tag has no usage guidance.
1,205
questions
1
vote
1answer
15 views
Define/store individual elements of Table output for back-substitution
At its core, mine is a very simple communication error between me and Mathematica that I haven't been able to crack, so I do apologise if it seems embarassingly inane.
Please consider the following ...
0
votes
2answers
25 views
Replacing function by another one each time it appears
I have expression involving Cos of some parameters. I would like to replace those Cos by their infinite series each time they do appear.
I tried the following which doesn't work:
...
0
votes
0answers
34 views
how to concatenate substitution lists
I'm solving a complex system of equations step by step. And for each of them, I get one of the four solutions q0, q1, q2 and q3, one at a time. Each time with a nice substitution list like :
...
0
votes
0answers
20 views
Different results when using ReplaceAll
Here's a riddle. I have a matrix QQsimple with some algebraic expressions. For example:
QQsimple[[36, 22]]
evaluates to:
...
8
votes
2answers
207 views
Given x ⊕ x =5,x ⊕ (y ⊕ z) = (x ⊕ y)+z-5 what is 2009 ⊕ 1949
There is an operation "⊕" that satisfies
$x ⊕ x =5$
$x ⊕ (y ⊕ z) = (x ⊕ y)+z-5$
what is 2009 ⊕ 1949?
I think it is feasible to solve with Mathematica, but my code doesn't give a useful ...
0
votes
1answer
43 views
Change Replace Rule with Function Input
I am trying to create a function that takes in an input $\mu$ and place that input into the replace rule for a numerical integration, as seen in the code below:
...
1
vote
1answer
80 views
Lévy C curve fractal from a substitution systems in NKS book p.190?
How can I make the geometrical transformation described in the page 190 in the New Kind of Science book by Stephen Wolfram to produce the fractal pattern?
https://www.wolframscience.com/nks/p190--...
1
vote
1answer
49 views
Substitution of expressions in a symbolic expression
I define tables of symbolic variables in the following form (for convenience)
...
3
votes
2answers
57 views
Renaming expressions dynamically in Mathematica
I am trying to write a statement that will create a new positionVector as I parse through a matrix.
What I am trying to accomplish would look something like this,
For[i = 1, i <= vectorlength, i++ ...
6
votes
4answers
486 views
Replace sum x+y+z in expressions like 2x+3y+z
Related threads replacing-a-sum-of-expressions and Replace a sum of squared variables by a new squared variable
Given the identity $x+y+z=p$ I'd like to simplify the generic expression
$$kx+ly+mz$$
...
3
votes
2answers
90 views
Creating an Array with Subscripts and Superscripts
I would like to figure out how to construct an array using subscripts and superscripts based on the following info:
...
0
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0answers
34 views
0
votes
4answers
60 views
0
votes
1answer
37 views
commutator between tensor products
I am interested in some quantum mechanical calculations in Mathematica. I am working with a tensor product of Hilbert spaces $\mathcal H = \mathcal H_1\otimes \mathcal H_2$. I would like to implement ...
3
votes
1answer
113 views
Replace in Mathematica [closed]
I have:
$$X=Z+22*Y$$
$$Y=P$$
Edited:
Is there a way to replace $Y$ in the first expression using Mathematica?
I tried Replace and it's not giving the desired result.
Can I replace both Z and Y at the ...
1
vote
3answers
70 views
My rule does not do anything (understandably)
I want a rule that would transform, for example, And[i,F[j,k],l,G[m,F[j,k],n],p] into And[i,F[j,k],l,G[m,T,n],p], where ...
7
votes
1answer
195 views
How to replace only the isolated variable x
I want to replace the variable x in the result, not x in unrelated x[i].
...
0
votes
1answer
29 views
Why does DifferenceRoot evaluate only in this table?
I would like to use a complicated function containing DifferenceRoot as a replacement rule, but somehow it evaluates only in ...
0
votes
0answers
49 views
How to plot a function using a table particular values
I would like to plot the following function in terms of kR, but using specific different values, I think the best easy way is using a Table. This is a common useful problem to explore numerical the ...
0
votes
1answer
52 views
Using MapThread and ReplaceAll together
I am trying to carry out some operations on the elements of dataset2, which is an 11 x 14 x 6 dimensional array:
I have a function, ...
0
votes
3answers
87 views
Pattern matching involving a sum of wildcards
I am trying to implement the following substitution to an expression in Mathematica:
ti den[a-ti] -> -1 + a den[a-ti]
where ...
3
votes
1answer
49 views
Replace Condition in Replacement Rules
In finding an answer to my other question, I'm finding myself needing to manipulate the conditions imposed on replacement rules, but this is proving to be a little difficult. In particular, how ...
1
vote
1answer
43 views
When numbers plugged in - this expression evaluates to zero, but otherwise will not evaluate to zero
I have the following code:
...
1
vote
1answer
55 views
ReplaceAll with a list of parameters [closed]
Trying to ReplaceAll with a list of parameters, but I can't see how to do it properly:
...
2
votes
1answer
45 views
How to protect the expansion of exponent while applyting rules
I am trying to separate/split an expression (consisting of polynomials) to a list. However I want to keep the exponents intact. Here is an example:
...
3
votes
1answer
212 views
Mathematica can't replace integer multiple of 2 in power
I have some terms contain
ww=a+a^2+a^6+a^-4
where
(a^2)^p_. -> -dx[p] Exp[-x[p]] x^2
but Mathematica only replace power 2 ...
7
votes
3answers
332 views
Applying a function to every item in a column of a matrix
A problem that arises more often than I care for is that I want to modify specific elements nested lists.
Examples may be wanting to add 1 to the second value, get ...
1
vote
1answer
52 views
Why does Replace `/.` not get evaluated in this formula?
Learning the wolfram Language, in section 32
"The Wolfram Language" // Characters[#]& /. Alternatives @@Characters["aeiou"] -> Nothing
...
1
vote
0answers
48 views
Simplification and patterns
I have a very simple simplification to make, where I need to do a replacement but the pattern matching seems slightly awkward.
I would like to simplify:
...
5
votes
3answers
146 views
Conditional replacement element-wise
I have a $4\times 4$ matrix (symbolic). It has a variable, say jj, which should be $1$ for diagonal and $0$ for non-diagonal entries. I need to write a replacement ...
1
vote
0answers
48 views
1
vote
0answers
22 views
Difference in pattern matching between Cases and ReplaceAll
I don't understand why there is a difference in the pattern matching between
x a /. coef_*x^pow_. :> {pow, coef}
and
...
2
votes
1answer
57 views
How to get the result in terms of a previously defined expression?
Say I have a vector
X[n_] := Table[Subscript[x, i], {i, 1, n}]
and a matrix of connections:
...
6
votes
1answer
119 views
How can I get the progressive application of list of rules?
I have a very long list of rules, and using this list of rules I want to see how some elements evolve as I successively apply the next rules on the previous rule.
Here is the simpler version of my ...
4
votes
1answer
97 views
Turn definitions into rules
I know that this seems to be unnecessary, but here I have a bunch of assignments, like around 50, and I want to create rules for all these to have the freedom to apply these rules only on certain ...
0
votes
2answers
77 views
How to solve for y for a set of implicit (in x and y) linear equations for use in Plot?
From a matrix m={{1, 1}, {-1, 1}}, a vector b={1, 2}, and a list of variables vars={x,y} we ...
0
votes
1answer
28 views
Is there a better syntax to obtain the derivative of a function as a function/operator? (e.g. for simple plotting of derivtives of functions, etc.)
When trying to plot a derivative of a function, (I take Sin as a simple example), the naive approach
...
3
votes
1answer
83 views
Replace multiple variables using a list?
I want to calculate sum of derivatives
of expression
F = Exp[(x*z - 1) f*b + (x - 1) (1 - f) b]
from n-th to (n-k)-th, say k=4. The dummy way which works is:
...
1
vote
1answer
49 views
Write function in terms of a combined variable [closed]
I am working with recursive convolutions of complex functions (fourier transforms), so, I calculate convolution integrals of functions of the form
$$g(iy) = \int_{-\infty}^\infty f(ix)f(i(y-x))dx, \ \ ...
5
votes
2answers
134 views
How do I replace specific sequences of a sublist without changing the level of the list?
Suppose I have a list of multiple sublists:
testlist={{1,1,1,0,0,0,1,1,1,0,1,1},{1,0,0,1,1,1,1,0,1,1,1,0}}
I want to replace given sequences without creating new ...
0
votes
0answers
66 views
How can I shuffle the indices of certain variables?
I am recursively defining rational expressions in two sets of variables $x_i$ and $y_i$. Specifically, for $m<n$, I am interested in replacing all degree-$m$ monomials of the following form: $$\...
1
vote
1answer
24 views
Error: Root::npoly: not a polynomial in #1 [closed]
I have a $45\times 45$ matrix $H$ and its elements depend on $Ca$. I want to find its eigenvalues (which will also depend on $Ca$). I do this using:
...
1
vote
2answers
44 views
How to define a series of substituting rules?
suppose I have a long list of many variables: alist = { u, v, w, ... }.
At some point, I have another combination of variables depending on { u, v, w, etc.},e.g.,
alpha = 2 * u + v
beta = v + w^2.
And ...
7
votes
4answers
202 views
How to use each replacement only once in a list of replacements
I have a list of replacements and some list they are acting on. However, some RHS of the replacements rules are identical (the LHS is not). I want to use those rules one after another (perhaps cycling ...
1
vote
2answers
42 views
How to match a formula in different level
Solve[4 n^4 + 4 n + 3 == 0]
The result has many
$$
\sqrt[3]{\frac{1}{2} \left(1+i \sqrt{3}\right)}
$$
so I want to replace them with a letter, for example , ...
1
vote
2answers
50 views
Swap two numbers - but only in a particular context
I have a list of terms such as {2*s[1,2]^2, 3*s[3,5]^4, ...} and I would like to have a replacement that swaps $2 \leftrightarrow 4, 3 \leftrightarrow 1$, but only ...
0
votes
1answer
23 views
How to define the correct replacement
I would like to replace a specific expression
denrule={Den1[vk]^e1_*Den2[l]^e2_*Den3[k+l-v*\[Omega]]^e3_*Den4[k]^e4_*Den5[kl]^e5_->j[MI,e1,e2,e3,-e4,-e5]};
The ...
0
votes
1answer
61 views
How do I make a substitution to an expression inside a derivative? [duplicate]
Pardon if I didn't ask the question correctly. Still trying to figure out the language.
I have the following expression:
$$energy=\frac{1}{2}R_s^{'}[t]^2==\frac{4}{3}G\pi\rho R_s[t]^2$$
...
4
votes
1answer
61 views
Generate a list of rules from two rules
I have two lists:
a = {a1,a2,a3}
b = {b1,b2,b3}
and I want to generate a list of replacement rules
...
2
votes
1answer
35 views
Formula: setting parameters vs replacement, different results?
I have a question that may sound stupid and have an easy answer - but I currently do not see it.
I have defined a function of four variables, $f[a,b,c,d]=...$, in what I think is correct Mathematica ...
