Questions about Mathematica's rule-based replacement functionality, including functions such as Rule (->), Replace, ReplaceAll (/.) and ReplaceRepeated (//.).

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2
votes
2answers
58 views

Derivative of Vectoral NDSolve Interpolated Function / Rule Solutions,/., and Vector NDSolve [duplicate]

I need to find the instantaneous phase and instantaneous frequency for a rotating system. I am having difficulty making the math work with interpolating functions. First, here is a problem without ...
5
votes
3answers
214 views

Simple image processing very slow

I have compared the speed of some simple image processing routines between Mathematica an IDL. 1. Reading of a grey scale png image of (720,577) pixels: The image is: Mathematica: ...
6
votes
1answer
171 views

Better replacement rules to perform this change of variables?

In cosmology, it is common to work with both a normal time variable t and a “conformal” time variable τ, which is defined such ...
3
votes
3answers
64 views

ReplaceImageValue and ReplacePixelValue extremely slow

I have a grey scale image: and I am doing the following: bin = Binarize[image, 0.18] ...
4
votes
4answers
111 views

How to replace all symbols except several?

I'm doing some heavy symbolic calculations and for preliminary simple tests I need to replace all coefficients except chosen with 1, e.g.: ...
4
votes
1answer
67 views

Is Replace doing double work?

In an answer to this question, rm -rf used the function Replace with level spefication to do a series of replacements inside out. As far as I can see, the order of substitutions when more than one ...
1
vote
1answer
83 views

What's wrong with this tutorial? [closed]

Disclaimer: This code is not mine. Source. I'm trying to follow along with it, though, but it seems that this code no longer produces a working manipulatable plot at the end -- and I'd like to know ...
0
votes
0answers
34 views

How to solve ReplaceAll problem inside Manipulate

I'm running into some trouble when I try and use Manipulate (code included below). Instead of letting me manipulate the plot, I get an empty plot and this: ReplaceAll::reps: ...
1
vote
0answers
34 views

Question on Function in Replacement Operation

I am trying to create a replacement function which, depending on the input, gives an additional minus. In my example I have an undefined function a with two ...
2
votes
0answers
84 views

Is this a bug in NCAlgebra library?

In course of my work with NCAlgebra package for Mathematica, http://math.ucsd.edu/~ncalg/ , I encountered unexpected behavior of replacements. I am using ...
4
votes
2answers
92 views

Remove redundant parameters from equation

I have random expressions like (b1 x + b2 x)/(b3 + b4/b5 x) + Sin[b6 x] where $x$ is a variable and {b1, ..., b6} are parameters to be fitted. This expression is ...
0
votes
1answer
108 views

Replacing powers of $n$-th partial sums in the output of a function with $S[i]$ for $i = 1,\ldots,n$

I've written some simple code that, for various $N \geq 1$ and $k = 1,\ldots,N+1$ computes the $n$-th derivative of $\log S_N$ where $S_N(z) = \sum_{k=0}^N \frac{1}{k!}z^k$ as follows: ...
2
votes
3answers
484 views

Replace all integers by 1?

Let list1 be a list of variables of the form {c1 a, c2 b, ...} where $a,b,...\in\mathbb{C}$ and $c1,c2,...\in\mathbb{Z}$. I am ...
2
votes
1answer
83 views

replace RHS of rule

is there an elegant way of replacing the RHS of a rule with the value of some function of it. Say I have {{a -> 1.2}, {a -> 2.3}} and I want to replace ...
2
votes
1answer
99 views

How to program a clickPanel for chemical elements (like a periodic table)?

The command ColorData["Atoms", "Panel"] indicates RGBColors of "Atoms" by clicking a panel. As I don't want to reinvent the wheel, I asked myself: How to ...
15
votes
2answers
204 views

Why Infinity /. _?(# < 6 &) -> 0 replaces Infinity with ComplexInfinity?

Suppose I define a matrix: mat = { {Infinity, 4, 9}, {6, Infinity, 10}, {8, 9, Infinity} }; Now I want to replace all values smaller than ...
8
votes
1answer
206 views

Transformation rule on a list of non-negative integers

I am trying to create a transformation rule that takes a list of non-negative integer values of any length, finds a non-zero entry in the list, adds 1 to all preceding numbers, subtracts 1 from the ...
4
votes
2answers
274 views

Replace x, but not x[a]

I want to replace all occurences of the symbol x with x[a], as long as it is not in the form ...
14
votes
4answers
1k views

How to change element color in Periodic Table?

The command ColorData["Atoms", "Panel"] generates a periodic table. As I don't want to reinvent the wheel, I asked myself how to change the color of each cell ...
3
votes
1answer
83 views

Why does the replace all (/.) evaluate differently in plot

I'm plotting this function: Plot[(2 (l/2 π)^2 ((2 π f)/c)^2 /. {f -> (f 10^9), l -> .01, c -> 3 10^8}), {f, 17.5, 26.5}] but it does not plot ...
0
votes
0answers
31 views

How can I replace an expression by another

I'm trying to replace a expression like this: (s[e,f] - I*phi[e,f]) -> M[e,f] Can anyone help me?
1
vote
3answers
118 views

A rule replacement problem: list -> list

Suppose I have a vector function f[x_] := {x[[1]]^2 - x[[2]]^2, Sin[x[[1]]] + Cos[x[[2]]]}; Then I want to make a list of gradients at some values: ...
1
vote
2answers
66 views

replace two elements in a list with the sum of those two elements?

I have a list: G[3] = {2, 4, 2, 4, 2, 4, 2, 4, 2, 4} (there's a 3 in there for the 3rd Prime) Recursively defined by: ...
1
vote
3answers
92 views

Randomly changing matrix entries

1.Write a block of code that generates a 4x4 matrix with randomized real number entries each between 0 & 1, then selects 3 matrix entries at random, and finally replaces these 3 entries with a ...
1
vote
0answers
105 views

Replace part in a matrix that matches specific pattern

I have the following problem. Given a matrix L which looks as follows, Matrix L is a link, route matrix. Further, I got the following vector (d), which indicates the demand per vertex combination. ...
1
vote
0answers
48 views

Understanding the order of applying Rule to expression [closed]

I am a little confused about: In what order is a Rule tried to apply to an expression? In a depth-first order or otherwise? For example, ...
1
vote
2answers
65 views

Replace list of symbols in an expression

I have an expression: exp = a+b+c and a list containing all the symbols of my expression: syms = {a,b,c} and I would like ...
5
votes
2answers
141 views

Apply Trig Identity to Transform Sum of Sinusoids into Phase-Shifted Cosine Function

I'm trying to solve for the output of a simple RC low-pass filter, with Cos[w t] input. The convolution of the input with the RC transfer function gives me the right output, but I'd like to be able to ...
27
votes
2answers
1k views

Best practice of passing a large number of parameters to functions

I have a number of functions that all take a large number of parameters. I am wondering what is the best practice of passing these parameters to those functions. I could, of course, simply specify ...
2
votes
3answers
71 views

How to get an element of a list , which is computed out of substituted variables?

What is the best way to get the element of a list, which is computed out of substituded variables? For example one wants to get the first element of the first row of ...
2
votes
2answers
35 views

replace an interval of values [duplicate]

I want to replace values in an interval [a,b] by 0 in a list of values. Example: {{.5,.2,.49,1,1},{.49,.5,.495,1}} I want to get: ...
3
votes
4answers
114 views

How to Remove Undirected Edges that are the Same [duplicate]

Given: theData = {1 <-> 2, 2 <-> 3, 2 <-> 1} I would like to remove any duplicates where I define a duplicate to be: ...
2
votes
2answers
63 views

Conditional replace of a column

Im trying to replace the value in the Nth column of a list if a condition is true, returning the modified list. I've tried modifying the answer from 61219 and been through most of related questions ...
5
votes
1answer
154 views

Conditional string replacement

I have a list of text and need to replace an element based on the text that appears in the element before it. Example of my list: ...
4
votes
1answer
99 views

Simplifying a b = 1 in non-commutative products?

Yesterday, I try to define some rules for non-communicative multiplication, here. I find some quite helpful rules, but things still do not work properly; the distributive rule can't be applied (e.g.: ...
12
votes
7answers
877 views
0
votes
1answer
66 views

Why Infinity edges with WeightedAdjacencyGraph [closed]

I can't understand why WeightedAdjacencyGraph wants Infinity weight when there are no edges between two nodes. In particular ...
0
votes
0answers
39 views

Replacing variable names in a notebook

I am working on a code that simply imports and graphs a function. If I preset the directory I would have something that looks like this: ...
3
votes
6answers
168 views

Change last column of a matrix

Given a (rectangular) matrix of integers, i.e. RandomInteger[4, {10, 3}] I want to apply the following rules only to the last column ...
0
votes
0answers
41 views
9
votes
3answers
304 views

How to replace the first occurance in an expression instead of replacing all?

Is there a function that replaces the first occurance of the expression instead of replacing all? For example, if I have HoldForm[x + 2 + 4 + x] /. x -> 4, is ...
5
votes
3answers
143 views

Assign output of solve to variables [duplicate]

I have this input: Solve[x^2 + 3 x + 2 == 0, x] which gives this output: {{x -> -2}, {x -> -1}} I want the first x ...
8
votes
1answer
275 views

Mma10 mystery: Failure of pure function substitution with Interpretation?

Bug introduced in 10.0.0 and fixed in 10.0.1 I had code to display with subscripts from Displaying index as subscript on output: e.g. C[i] -> C_i with Notation[...] or Interpretation[..]? which ...
1
vote
1answer
91 views

Function returned an unexpected list

I was trying out a question in Wellin's Programming with Mathematica that says the following. Question: Given a set of points in the plane (or 3-space), find the maximum distance between any pair of ...
3
votes
1answer
53 views

Select a Placeholder in a Notebook?

How might I select the 1st Placeholder in a Notebook? SelectionMove Has no option. ...
2
votes
1answer
65 views

Add to the last digit a number

I have data from a Multimeter that has a precision of 0.6%rdg+4dgt. So i want to take the last digit of, say, 12.007 and add 4 to the last digit like ...
0
votes
1answer
51 views

Speeding up ReplaceRepeated while truncating to desired order

I need to program in an algorithm that recursively makes algebraic replacements which leads to an utterly complicated algebraic function of $x$, but whose final result is only needed at fixed order in ...
3
votes
3answers
181 views

Transformation of Derivatives under change of coordinates [duplicate]

I have an expression depending on the two variables z and t, and the derivative of a known function $f(t,z)$. Something like: $$myexp \ =\ t\ z\ \partial_z\ f(t,z)$$ Now I want to make a change of ...
0
votes
0answers
77 views

Using one complicated equation to reduce another

(Relative noob here so don't assume much!) I need to use a vector equation (with $N-1$ entries) in the general form $y_j(x_{i,j},x_{i,j+1},x_{i,j-1})=0, i=1...3, j=1...N-1; x_{i,0}=x_{i,N}=0$, ...