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

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2
votes
0answers
110 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
122 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 ...
2
votes
3answers
503 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
139 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 ...
3
votes
1answer
116 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
234 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
223 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
296 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 ...
3
votes
1answer
108 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
35 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
153 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
79 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
106 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
126 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
57 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
110 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 ...
6
votes
2answers
227 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 ...
29
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
46 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
134 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: ...
3
votes
2answers
74 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
177 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
130 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
958 views
0
votes
1answer
95 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
44 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
172 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
10
votes
3answers
332 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
265 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
283 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
93 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
64 views

Select a Placeholder in a Notebook?

How might I select the 1st Placeholder in a Notebook? SelectionMove Has no option. ...
2
votes
1answer
69 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
57 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
263 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
88 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 $y_j(x_{i,j},x_{i,j+1},x_{i,j-1})=0, i=1...3, j=1...N-1; x_{i,0}=x_{i,N}=0$, ...
9
votes
3answers
1k views

Replace expressions with symbols

First of all: I'm new to Mathematica, so I would appreciate it if the answers are quite complete. I have the result of calculation that is expressed in $\sin$ and $\cos$. Now, all of these can be ...
0
votes
0answers
32 views

How to prevent function from substituting the part of the parameter name if it has a subscript? [duplicate]

I have the following problem, when defining and using a function, that's supposed to have an outside parameter xmin: A[x_] := Exp[-x/Subscript[x, min]] A[5] ...
1
vote
3answers
149 views

How to ReplaceAll independent of depth?

I have a big list which in principle can be described as this more compact list : ...
5
votes
1answer
194 views

How can I make a “self-referential” replacement operation self-contained?

Fairly often I find use for replacement rules that call themselves on the right-hand side of the rule, e.g.: ...
0
votes
3answers
86 views

Unexpected behavior of rule-replacing with string concatenation [closed]

Here's the code. Clear[x,y,z]; {x,y,z} /. x_ :> ("^_^" <> ToString[x]) I get the result ^_^{x, y, z}, which is not ...
1
vote
1answer
85 views

How can I write a function which takes another function of a variable and the variable itself as arguments and gives a list of critical points?

This is an exercise from Power Programming with Mathematica by Wagner. I need a function which takes a function and a variable as arguments, like this: critpts[f_,x_]:= and then on the rhs I've got ...
3
votes
4answers
208 views

Replace all symbols in a matrix with their numbered forms

I have a matrix made mostly from "x" with a few 0's thrown in: ...
3
votes
3answers
88 views

Replacing a sum of expressions

I have an equation which Mathematica solves but gives a huge output. However I notice in this output that the same expression occurs many times. Namely: $E=864 a^6 - 432 a^4 b^2 + 54 a^2 b^4 - b^6 + ...
8
votes
3answers
171 views

Substituting values in 3j symbols

I believe these three expressions should give the same answer of -1/Sqrt[3], but the first gives +1/Sqrt[3] whereas the second ...
1
vote
1answer
149 views

Solving equations with QuantityVariable

I'm trying to understand how to easily solve equations that use QuantityVariable. Why does this fail? ...
5
votes
3answers
265 views

When I use Rule, why doesn't this work?

k.k.k //. {k.k -> k} works perfectly, so the output is just k. But, when I use ...