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

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2
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1answer
111 views

Replace an expression with a slightly tricky LHS transformation

I would like to make the substitution x^(11*y) -> r in the following equation x^(11 *y^z) - 1 to end up with: ...
2
votes
1answer
64 views

Unique[] in RHS of rule

I have a function, explicit that takes dot product of two symbols, and replaces it with repeated dummy indices generated by ...
2
votes
1answer
200 views

A Sierpinski-ish structure, via 2D automata

The project is originally based on a puzzle proposed by EIORU at http://www.ptt.cc/bbs/puzzle/M.1342451949.A.00F.html (若您懂得讀中文 / if anyone happen to read Chinese^^) last July. The descriptions, ...
2
votes
2answers
31 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: ...
2
votes
3answers
67 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
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 ...
2
votes
2answers
62 views

Pattern evaluation in nested function call

I'll put the question right here, but will add some context below in case someone wonders why the heck I'm trying to do this. Why is it that I have to do two passes to get the value of the arguments ...
2
votes
1answer
62 views

Ordering for Pattern matching in Subscripts

I have some transformation rules acting on subscripted variables. When I match the a product the order matters. ...
2
votes
2answers
183 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
1answer
88 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 ...
2
votes
2answers
372 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+ ...
2
votes
1answer
81 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 ...
2
votes
2answers
135 views

Generating an editable table that can be used as input

Say I have a number $n_{max}$. I want a command to generate a table like 1 1 2 2 3 3 4 4 ... nmax nmax where the second column is editable, and this table can be ...
2
votes
1answer
79 views

Convert Integer to Numeric with Replacement rules

I have a long list of triples, each looking something like {AGO, 1988, 2345.23}. Some of these, however, have an integer in the third spot, like this: ...
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: ...
2
votes
1answer
130 views

How to transform an expression using algebraical instead of pattern rules [duplicate]

I would like to transform rules algebraically. A very simple example would be: - k^2 - 2 k x + x^2 /. {2*k -> 1} This transforms to: - $$k^2-2 k x+x^2$$ ...
2
votes
1answer
145 views

#[[1]]//FullForm = 1?

I have a set of symbolic algebraic expressions that I'm trying to get some speed into. To illustrate the issue, I'll use a simple form like { k0 X, k1 Y, k1 Z}, ...
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 ...
1
vote
4answers
187 views

How to find all symbols in an expression and perform an operation on them?

========== motivation =========== Suppose, for example, I have an incoming expression like m = (3-I)x + 4(x y)/(Cos[y]) I want to find all the symbols in ...
1
vote
1answer
126 views

Simple rule appears not to work

I have the following simple code ...
1
vote
2answers
69 views

Replacing a specific pattern of values at level 2 in a list

I've a list of lists, tl = {{True, False, m12}, {False, m22, m33}, {m32, False, True}} and each nested list has the same length, What is the proper way to ...
1
vote
3answers
121 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 ...
1
vote
2answers
164 views

Using patterns in ReplaceAll to extract elements from tuples at arbitrary depths

Please consider the following: I need to extract from MyList all last parts of each 3-tuple. ...
1
vote
2answers
188 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 ...
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: ...
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: ...
1
vote
3answers
174 views

Help me to find a way to do this repetitive stuff

I'm trying to do this: ...
1
vote
3answers
126 views

How to ReplaceAll independent of depth?

I have a big list which in principle can be described as this more compact list : ...
1
vote
4answers
112 views

Replacing more than one element from a Sublist

The following expression allows me to extract the value of x and y: ...
1
vote
2answers
104 views

How to define a rule to simplify the notation for derivatives of chain rule?

Suppose that $u(x,y)$ is a function, and $x=r \cos t$, $y= r \sin t$, then we can define a new function $v(r,t):=u(x,y)$ with $x,y$ replaced by the above equations. It is quite easy to compute $v$'s ...
1
vote
1answer
87 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 ...
1
vote
1answer
106 views

Matrix/tensor addition behaving funny under replacement?

I have two matrices I want to add, and one of the matrices is a tensor product of two vectors. I've used a SetDelayed to define the summed matrix, because I want to evaluate it for different values of ...
1
vote
2answers
92 views

How to “reversely” replace definitions?

I have the following problem at hand. 1.) I have a list of definitions like ...
1
vote
2answers
283 views

How to debug error triggered by replacement rule?

The second line below produces the errors shown: ...
1
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1answer
75 views

Solving equations with QuantityVariable

I'm trying to understand how to easily solve equations that use QuantityVariable. Why does this fail? ...
1
vote
2answers
107 views

Looking for an elegant way to solve a (system of) ODEs/functional equations with undetermined coefficients

I want to solve an ODE using undetermined coefficients/guess-and-verify and am looking for an elegant way to use this technique. I am running into a few ugly warts. Here is a basic implementation for ...
1
vote
3answers
174 views

Conditional Check on Matrix

Suppose I have the following matrix (i,j): ...
1
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2answers
93 views

How to get a rule for, e.g., (x + y) to apply to (-x - y), etc.?

For example, the substitution (x + y) -> s fails here: In[1]:= (-x - y) /. (x + y) -> s Out[1]= -x - y Of course, I ...
1
vote
2answers
66 views

How do I avoid vector variables being treated as scalars in the course of replacements?

I often work with a mixture of symbolic and concrete values as I develop teaching materials. I introduce variables symbolically and then need to instantiate them to specific values while continuing ...
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 ...
1
vote
1answer
2k views

Converting polar coordinate expression to cartesian coordinates

An intermediate step in my analysis requires me to work in polar coordinates, but I would like to convert the results back into cartesian coordinates. The conversion is very simple but tedious for ...
1
vote
1answer
75 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 ...
1
vote
1answer
35 views

Automatic substitution of fractions

I have several equations with many variables, and here and there I would like to do a variable substitution. For example, in the equation: a (b + 42 c / d) I ...
1
vote
1answer
83 views

Nest Replace Function with different rules

I have a table of data that I want to filter. Any value of zero in the table means that value was not calculated, so it should get populated with the tag "NC". Next the table is filtered for all ...
1
vote
4answers
72 views

Replace a sum of squared variables by a new variable squared

Is there any way to tell Mathematica to replace $\kappa^2 + k_z^2 \rightarrow k^2$ in an expression? I want to make a result more readable, e.g. something like this: $$\frac{2 k_z^3 \sqrt{k_z^2 + ...
1
vote
1answer
107 views

Matrix substitution

I'm newbie in Mathematica and would like to ask one simple question. Let's say I have matrix with some elements == -1 ...
1
vote
1answer
45 views

Different ordering for KroneckerDelta?

I have an expression like this: Assuming[m [\Element] Integers && n [\Element] Integers, 1/2 I J n (4-m n+n^2) KroneckerDelta[m,-n]]//FullSimplify Now, ...
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 ...
1
vote
3answers
123 views

Auto simplifications of power products

Mathematica automatically simplifies Exp[a]Exp[b] to Exp[a+b]. The problem is now that I can't do this ...
1
vote
2answers
50 views

How do I format expressions so that replacement rules correctly apply to exponents? [duplicate]

I have a series of rules that I would like to apply to a series of expressions with variables, but cannot get Mathematica to correctly recognize that these rules should apply when my variables have ...