Questions tagged [replacement]
The replacement tag has no usage guidance.
1,474
questions
4
votes
2
answers
47
views
Replacement question
I have this equation
F2 + F4 - V1 + V3==0
I want it to be converted automatically via a replacement rule to
...
- 1,203
1
vote
2
answers
211
views
How to define replacement rule for Minkowski inner product
following question,
I have an expression that consists of several Minkowski inner products between 2 four vectors written as in Mathematika:
...
- 21
0
votes
0
answers
29
views
Get Complete form of a function from a nested definition [closed]
I have pretty basic question. Assume the Following system:
F[x]:=2*x
G[x]:=2*F[x]
How do I substitute F[x] in ...
- 101
2
votes
2
answers
81
views
Replacing symbolic variables inside of a compile
As the result of a symbolic integration, I have a very long array with symbolic variables u[i] which I would like to substitute for real number values. Moreover, I ...
- 43
0
votes
0
answers
29
views
Simplifying a Given PDE Expression [closed]
I have an expression for the $2D$ velocity of a fluid, given by:
$$ \vec{u} = -(k+k_0)[\nabla p-\frac{\delta \mathcal{F}}{\delta \phi}\nabla\phi]-k_0(1-\phi)\nabla\frac{\delta \mathcal{F}}{\delta \phi}...
- 221
0
votes
0
answers
24
views
Non-Dimensionalizing PDEs using Mathematica [duplicate]
I am attempting to non-dimensionalize the following equation:
$$ \vec{u}=-(k+k_0)\left[\nabla p -(f'(\phi)-\epsilon^2\nabla^2\phi)\nabla\phi \right]-k_0(1-\phi)\nabla(f'(\phi)-\epsilon^2\nabla^2\phi)-\...
- 221
2
votes
3
answers
91
views
Replace repeated items differently
So I have a simple replacement rule of the following form:
expr/.f[a_,b_]:> g[a,#]g[b,#]&@func[]
i.e. I want to replace each function f[a,b] with two ...
- 651
3
votes
1
answer
76
views
Transforming A Complicated Expression
I am trying to transform an expression according to these rules I've defined:
$$
L_1^m L_2^n L_3^p L_4^q \rightarrow \frac{m!n!p!q!}{(m+n+p+q+3)!}6V \\ \text{constant } k \neq 0 \rightarrow kV$$
Some ...
5
votes
1
answer
108
views
Function with optional argument that depends on other argument
I'm trying to do a simple thing: I want the optional argument to depend on another argument, i.e.
f[x_,y_:Subscript[m,x]] := x-y
This should give: ...
- 651
4
votes
3
answers
265
views
Simplify with given equality
Clear[id, kn, vt, vdd, vo];
id = kn*(vi - vt)^2/2;
vo = vdd - id*rd;
Solve[D[vo, vi] == -1, vi]
Output:
...
- 143
3
votes
2
answers
145
views
How to replace generic function with another one?
I have complicated expression in terms of derivatives of a multivariable function F[x,y,z] say
...
- 33
0
votes
1
answer
86
views
Replacing a term according to a given criterion in an expression with non-commutative multiplication (for any sign and location)
There is the following expression:
...
- 1,881
1
vote
2
answers
98
views
Replace with non-commutative product
I'm trying to evaluate some scattering amplitudes terms in Mathematica using the spinor helicity formalism. For that, I need to turn products like $\epsilon_i\cdot k_j$ into spinor product which can ...
- 209
19
votes
1
answer
743
views
When did this global rules change happen in Mathematica? Is this change documented?
In this Wolfram talk video titled "Professor Richard J. Gaylord's Wolfram Language Fundamentals Part Two" he shows at time 36:45 the following
Where there are two definitions for ...
- 115k
2
votes
1
answer
54
views
How to do the following symbolic substitution?
In the algorithm that I am trying to implement, I have the following symbolic substitution to be done $z^{-2 n} \rightarrow \frac{(i t)^{2 n-1}}{(2n-1)!} $.
I tried to do the above as
...
- 155
3
votes
1
answer
75
views
How to Programmatically Replace a Word in a Text Cell with a Button (for popup definitions)
I am attempting to create popup definitions for important words in my lecture notebooks. I plan to create a glossary containing a list of words and their definitions and then search through my lecture ...
- 4,825
0
votes
0
answers
37
views
Finding variables that are arbitrary (undefined) functions of other variables with arbitrary names (such as n1, n2,n3)
I have expressions that could look like:
$$ n = n0 + n1[x,\tau_0, \tau_1]+n2[x,\tau_0, \tau_1]+n3[x,\tau_0, \tau_1]+ \dots$$
Where the $n_i$ are undefined functions of the variables listed inside ...
- 1
1
vote
1
answer
54
views
2
votes
1
answer
63
views
1
vote
0
answers
53
views
How to get rid of "/." in my result, when I evaluate a term containing ReplaceAll?
In the previous code I defined Bchoice and pchoice
In one line I defined
...
- 111
6
votes
3
answers
251
views
Replace items of list except items that are member of another list
I want to replace all items in li1 that are not members of li2 with x.
...
- 3,735
0
votes
0
answers
32
views
Algebraic substitutions not working? [duplicate]
I have been trying to simplify this matrix
$$
\left(
\begin{array}{cc}
\frac{1}{2} \left(-2 g \sqrt{1-\text{tauA}} \sqrt{1-\text{tauB}}+\text{mu} \text{tauA}+\text{mu} \text{tauB}+\text{...
2
votes
2
answers
55
views
Why is first substituting for the known variable and then solving for an unknown variable, using Solve[], correct whereas doing the reverse is wrong?
Consider the following code:
(*Initializations*)
c=10;
f=Log[1+c]-c/(1+c)
I am trying to figure out whether I should first substitute for ...
- 21
0
votes
0
answers
43
views
Transforming $e^{m i\beta+n i \gamma}$ into $x^m y^n$
I want to write code to transform $e^{m i\beta+n i \gamma}$ into $x^m y^n$, where $m,n\in \mathbb{Z}$.
For example, I write the follow code when $m=3,n=2$:
...
- 137
4
votes
1
answer
85
views
How to generate a list of lists from a given list following a rule recursively?
Assume that I have made the following rule:
Rule:
{x1,x2,x3,x4,x5,x6,x7,x8}
-> {x1,x2,x3,x4,x5,x6,x7,x8}, {x4,x5,x6,x1,x2,x3,x7,x8}, {-x1,-x2,-x3,-x4,-x5,-x6,x7,x8}, {x1,-x2,x3,x4,-x5,x6,-x7,-x8}...
- 2,151
5
votes
3
answers
275
views
Making algebraic substitutions with approximations
I'm struggling to make a substitution in a symbolic expression where I want to use an approximation. For example if we have the equation
$$\frac{1}{a}\frac{c}{a - b} = \frac{c}{a^{2} - a b} \approx \...
- 2,366
21
votes
3
answers
1k
views
What is the fastest method to set the diagonals of a matrix to 1?
I am trying to replace the zeros along diagonal of a distance matrix to a list of constants. In this case, a diagonal of 1's.
It appears that the LinearAlgebra ...
- 2,779
0
votes
0
answers
58
views
Back-substitution
Suppose that we have an expression (expr in the code below) and replace a long term with a new parameter (K).
For a simple example;
...
- 507
1
vote
1
answer
56
views
function/module to achive a replacement as follows
I want to shorten some long expressions by using some new parameters. So, I want to
create a function/module to achive a (multiple) replacement as follows:
...
- 507
3
votes
1
answer
93
views
Use rules on list elements one by one [closed]
I have two list
list1 = {1, 1, 2, 4, 1, 1, 8, 7};
list2 = {a, b, c, d, e, f, g, h};
I want to build rule,...
- 885
1
vote
1
answer
33
views
Keep arguments of a function unevaluated after replacement rules
Consider an expression of type
f[a,b]+a+b
and a set of replacement rules
sub={a->1,b->2}
If I evaluate now the ...
- 131
1
vote
0
answers
27
views
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
31
views
Using ReplaceAll to simplify derivatives
I'm struggling trying to simplify the derivative of a function. I know that ReplaceAll works like that:
What I want is to replace the function itself that should ...
1
vote
2
answers
51
views
How can I collect the sum of any number of gradients without using ReplaceRepeated[]?
Recently, I have run into the problem where I need to collect the the sum of any number of gradients. I have defined a function grad[] to represent the gradient, ...
- 443
0
votes
0
answers
38
views
How to replace functions with their Fourier transform [duplicate]
I have a function \deltaG given by
...
7
votes
8
answers
452
views
How to replace anti diagonal elements of a matrix
I want to assign new values to the anti-diagonal elements of a square matrix m with the values of its diagonal elements. For that, I want to make use of ...
- 319
3
votes
2
answers
125
views
Replacing a trigonometric value
It looks like MMA cannot evaluate Tan[42°] but it can be written as
(-Sqrt[6 - 2 Sqrt[5]] + Sqrt[6 (5 + Sqrt[5])])/(2 Sqrt[7 - ...
- 1,273
4
votes
1
answer
44
views
Timing Discontinuity with Replace[] Function
When constructing certain square matrices I noticed a sharp jump in the time required to build them. I've included code and a plot of time required to make the matrix vs dimensionality of the matrix. ...
- 187
5
votes
4
answers
581
views
Replacing large numbers
Imagine I have the following list
l = {{1,2,3},{4,10^(16),5}}
How do I efficiently replace the large number by a number (zero, for example). I can't seem to do it ...
- 4,388
8
votes
2
answers
116
views
Constructing a RootSum object changes existing internal syntax
Bug introduced in 9.0 or earlier and persisting through 13.0.1 or later
I noticed that initially valid syntax becomes invalid within nested RootSum objects. ...
- 2,939
4
votes
3
answers
211
views
How to use a rule such that it substitutes the value x and derivatives of x in the expression?
For example, I have gotten the value for a certain function H[t,r]:
$H[t,r] \to -\frac{2r(K[t,r]+K^{(0,1)}[t,r]+2m+r+...)}{(2m-r)}$
I want to replace its value, ...
8
votes
2
answers
313
views
Simple, fast re-defining a part of 2D list
A[[{2, 3, 5}]] = {97,98,99}
changes 2,3,5-th elements of A to 97,98,99 respectively.
Similary
A[[{2, 3, 5}]] = 100
changes 2,3,...
- 3,221
2
votes
1
answer
28
views
MatchQ returns False for a match for e1 ** e2 while matching both e1 and e2
I used a simple predicate realQ[x_] := MemberQ[{Real, Integer, Rational}, Head[x]]. With that predicate
both ...
- 21
2
votes
1
answer
58
views
Can substitution rules be used in function definitions?
Simple input like this
f[x_]:=2x
f[2]
has the predicted output of 4. However, this
r={a->2x};
f[x_] := a/.r
f[2]
Produces ...
- 187
0
votes
1
answer
58
views
FindFit with Replace error
I am trying to fit my data, and I keep having error messages as below. Could anybody help me to solve this problem? The codes are written after the error messages.
...
- 15
3
votes
1
answer
75
views
Terms of expressions with non-commutative multiplication that meet the given criteria
There is the following expression:
expr=a^3**x**Transpose[x]**y+x+y**Transpose[y]**x**a^3+x**Transpose[y]
It is necessary to apply the ...
- 1,881
7
votes
7
answers
425
views
'Mapping' the values of a list to variable
Suppose I have the variable expr1 = a[n] + b[n], and the list stencil={-1,0,1}. I want to make a function ...
- 957
0
votes
0
answers
41
views
Replace Derivative[ i ][ f ][ t ] with f[ i, t]
Assume the PadeApproximant is carried over f[t0] * g[t0] with the order {1, 1}, that is
<...
4
votes
2
answers
189
views
Tropical Operation Conversions: Multiple Operations
I apologize if my syntax is bad. I looked around, but didn't see anything on this in the stack exchange.
I would like to be able to transform a classical real-valued polynomial to a tropical ...
- 143
4
votes
1
answer
75
views
Replacement, PatternTest, Module related Question
Let's see how MMA handles following type of expression :
Replace[L, {pattTest1->rhs1, pattTest2->rhs2, pattTest3->rhs3}, {1}]
Specific example :
...
- 3,221