Tagged Questions

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

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0
votes
1answer
93 views

Function generating a rule with a Patterns: e.g. toRule[ lhs, rhs] into lhs[x_] -> rhs [duplicate]

I want to create a rule as a function of z from a left and right hand side. My (non-working) code and usage is: ...
5
votes
0answers
197 views

Is everything in Mathematica ultimately stored as a rule?

My current understanding about Mathematica is that everything, at the lowest level, ends up as replacement rules. First question: is this true? Second question: does Mathematica "gloss over" these ...
4
votes
2answers
119 views

BezierCurve in EdgeShapeFunction fails when used on multiedges graph

I would like to create a network graph with curved edges. To do this, I wrote this function: ...
2
votes
2answers
131 views

How to plot complex values given by Solve

Update Solve[N[Table[BernoulliB[n, z], {n, 10, 10}] == 0]] ...
4
votes
3answers
153 views

Simplifying expression with patterns (Replace)

Q1: I need to simplify some algebraic expression, according to particular pattern, namely: \begin{equation*} x^m = \left\{ \begin{array}{ll} 1 & \text{if } m \text{ is even} \\ x & \text{if ...
4
votes
4answers
140 views

Rearrange graph

I have to rearrange graph described by j = {1 -> 2, 2 -> 3, 3 -> 1}; appling some function to all vertices on the right so rearrange[j] output should ...
1
vote
1answer
79 views

An equivalent in Mathematica [duplicate]

Let's say I have a $n$x$m$ matrix $M$ in Matlab and I want to substitute the elements of $M$ that exceed $15$ for $-1$. In Matlab I just write M(M>15)=-1 and ...
11
votes
4answers
312 views

How to replace every possible $A+B$ and $AB$ in expansion of $(A+B)^{10}-A^{10}-B^{10}$ with $x$ and $y$, respectively?

I would like to replace every possible $A+B$ and $AB$ in expansion of $(A+B)^{10}-A^{10}-B^{10}$ with $x$ and $y$, respectively. How to do it with the simplest code in Mathematica? For example, ...
0
votes
1answer
69 views

Manipulate that remembers its own input code and can show it by request

This question is a further question to my previous one. The solution for that question works well as long as the original input Manipulate code is still provided in ...
1
vote
2answers
192 views

How to replace subscript symbols

I have an expression with subscripted variables. I would like to replace all those terms with other symbols. For example, $P_1 + P_2^3 \rightarrow P1 + P2^3$ I used the following code but it doesn't ...
3
votes
1answer
152 views

Is there a way to simplify this replacement rule

I have a rather big expression which contains many sums of form q x + w y. I know that y is much smaller than ...
0
votes
1answer
98 views

Problem with List Dimension Outer Map [duplicate]

I am currently handling a big list which has the following dimension: {6, 3, 4, 2, 2, 1, 8} where the last number 8 represent a ...
3
votes
1answer
104 views

obtaining real roots of negative numbers in a long expression [duplicate]

I have a complicated symbolic expression which contains many terms like $(a/(a-2))^{1/m}$, where $a/(a-2)$ could be positive or negative after replacement. I only need the real root after ...
3
votes
3answers
389 views

StreamPlot using NDSolve gives error messages

StreamPlot[{x[0], x'[0]} /. NDSolve[{x''[t] == 1, x'[0] == v0, x[0] == x0}, {x, x'}, {t, 0, 1}], {x0, -2, 2}, {v0, -2, 2}] The above code gives me the errors ...
1
vote
2answers
290 views

How to debug error triggered by replacement rule?

The second line below produces the errors shown: ...
0
votes
1answer
144 views

Checking differential equation solution

I have this differential equation: eq=D[ψ[r],r]+A*ψ[r]-(B/(A*r))ψ[r]==0; And DSolve sucessfully solves it: ...
2
votes
2answers
185 views

Applying rules with functions to expressions with derivatives

I have a function that I want to see applied, potentially within a derivative. The use of delayed vs. non-delayed rules seems irrelevant. See the following: ...
2
votes
3answers
176 views

How to manipulate log arguments?

A common problem I have with Mathematica is needing to manipulate the arguments of logarithms. Typically, I need to take ratios of the log arguments Mathematica gives me by default. That's to say ...
1
vote
3answers
122 views

Replace inside a Held expression separate context

How do I replace content inside a Held expression without local values coming through? For example if you run the following code you get g[2] instead of ...
4
votes
3answers
146 views

Appending to sublists using “anchor” values

Say I have a set of lists that look like this: ...
3
votes
2answers
202 views

Can I ask Mathematica to replace the arguments of my functions with a replacement rule?

I have an equation that I evaluate at some point (let's say $x=1$) that have terms of the form f[1,y] D[g[1,y],{y,2}] Is there an easy way to replace [1,y] by ...
0
votes
2answers
179 views

Writing intelligent replacement rules for symbols

I am learning about quaternions right now, and I wanted to play around with some concepts I am learning. e.g. take rotation of a point about an axis with specified angle. ...
4
votes
1answer
208 views

How to speed up calculations with large number of replacement rules?

In my program I have an expression which looks like: ...
2
votes
1answer
161 views

Add Pattern to List Removing Duplicates

Lets say I have a list of patterns ...
1
vote
0answers
45 views

Best way to power series expand in multiple variables? [duplicate]

A power series expansion of a multivariate function can be performed with the Series command, which performs each expansion consecutively. The results can be a bit ...
0
votes
1answer
79 views

Scope of expression in a user-defined function

I have the following code: fbasic = A + R + Z*Z *Z*Z; f[A_, Z_, R_] := fbasic + R; f[0, 2, 3] The answer I am getting is ...
1
vote
2answers
77 views

Changing all link destinations in a notebook

I have a bunch of cells containing text and hyperlinks. i.e. of the form: ...
10
votes
3answers
495 views

How to properly project a Graphics object consisting of line primitives

My problem starts from attempts at depicting overlapping lines of different thickness, i.e. ...
2
votes
1answer
89 views

Replace inverse function

I'm solving an expression like so: Solve[u[x] == u[a] + u[b], x] Mathematica returns {{x->(u^(-1))[u[a]+u[b]]}} If I ...
1
vote
1answer
127 views

Simple rule appears not to work

I have the following simple code ...
3
votes
1answer
111 views

How can I avoid this ReplaceAll trap? [duplicate]

I am having some difficulties with the ReplaceAll function. When I write: {1, 2, 3, 4, 5} /. x_?OddQ -> x^2 I expect: ...
2
votes
1answer
134 views

Strange behavior when replacing variables by numerical values [duplicate]

I have a rather complicated function with parameters {a, b, c, d, e, f, k}, and I'd like to know its behavior as a function of k alone given other parameters, so I try the following code: ...
1
vote
0answers
125 views

Variable scope in nested NMaximize, NMaxValue

I'm trying to use NMaxValue inside other statements (FindRoot and NMinimize). Those statements should bind variable names, but I'm getting weird warnings which seem to indicate that the variables ...
6
votes
5answers
208 views

Lowering the degree of an polynomial with an assumption that the polynomial has a factor x^2+ax+b

Let's assume $ x^{10}+x^5+1 $ has a factor $x^2+ax+b$ Then, If $x^2=-ax-b$, $ x^{10}+x^5+1 =0$. If we successively apply $x^2=-ax-b$ to $ x^{10}+x^5+1 $, we can make $ x^{10}+x^5+1 $ to degree 1, ...
1
vote
1answer
209 views

Equating and solving equations that have been generated using table[]

I am in the process of trying to use Mathematica to find the coefficients of transmission and reflection for the wavefunction of a beam of particles tunnelling across any number of identical potential ...
2
votes
0answers
103 views

Generalization of a rule to N arguments

I am trying to apply a series expansion on a function x[t1,t2,...tn], with an expansion parameter a. For ...
3
votes
1answer
163 views

Shortening the syntax {var1, var2} /. # & /@ list

I noticed that I often turn out to have a list of substitutions in the form ...
-1
votes
1answer
80 views

How to make rules for changing parameters

I have one boring problem with changing parameters in printing output. If I have equation ...
1
vote
3answers
88 views

How can you form a variable from a function and its arguments?

Is there a way to make the general replacement foo[x,y,z]->fooxyz so that I can treat the x_i as variables so that I will obtain foofgh from the following: ...
13
votes
1answer
460 views

rule-based implementation of an algorithm

When I first started learning about rule-based programming with Mathematica, I tried to translate this algorithm for computing the convex hull of a set of 2-D points in $O(n \log(n))$ time, to use ...
1
vote
1answer
148 views

Improving the plotting time of a very complicated expression

The quatity $R$ is defined by a complicated expression in terms of $a_1,a_2,\ldots,a_n$. Now each $a_i$ is a function of $x$, $a_i(x)$. I would like to know what is the most efficient way to ...
17
votes
3answers
285 views

Options which require RuleDelayed

For some functions in Mathematica it is important to use RuleDelayed. One prominent example is the EvaluationMonitor for ...
1
vote
0answers
60 views

Abridging Lists of Equations within NDSolve, Manipulate [duplicate]

I have a pretty little NDSolve function that I've finally decked out with manipulatable (by sliders) coefficients, which changes the graph in real time. However, I ...
9
votes
1answer
252 views

Performance of Dispatch and lists of Rules

The issue outlined here seems to be no longer present in version 10, if you use a Dispatch table! This because a Dispatch table ...
9
votes
3answers
245 views

substitution rules excluding subscripted variables

Suppose I have an expression containing p,Subscript[p,1],Subscript[p,2],etc. I want to ...
5
votes
1answer
138 views

How can I substitute something using only map?

For example, I have the equation x^2 + y^2 == x*y and I want to apply the rule y -> s*x I can do it easily by ...
9
votes
2answers
488 views

Simple problem with Manipulate and Plot

Would anyone have an idea why the following doesn't work: rule = {z -> x^2 + 2 x + y}; Manipulate[ Plot[z /. rule, {x, 0, 10}], {{y, 2, "y"}, 1, 5} ] But ...
2
votes
2answers
381 views

Mass Symbolic Manipulation with Subscripts? (from plaintext Input)

The simplest example of the change being sought is a greek letter, typed in as plaintext nu, and its may be replaced by the symbol, ν: expr = 3nu*kx*ky+ ...
11
votes
4answers
346 views

“Strange” behavior of Rule

According to the Help lhs->rhs evaluates rhs immediately. How to understand the output of the following code? ClearAll@x; {1, 3.5} /. x_?IntegerQ -> {x} ...
0
votes
2answers
77 views

Replace expression using a tuple

Given an expression in x, y, z (for example), and a list with three elements, like ...