Tagged Questions

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

112 views

Better use of pattern matching in replacing elements of a list

I have a list of reals and I'm replacing those which are contained in a given interval with two different values depending on wheter the selected reals are positive or negative. I came up with this ...
96 views

Transformation rule for arbitrary number of argument expressions

I am failing to write a Mathematica transformation rule that replaces e.g. f[a + 3, b + 3, c + 3] with f[a, b, c] + 3 for an ...
61 views

Why does the replacement /. {1 -> x} make sense?

Why does the replacement expr /. {1 -> x} in which the number 1 is replaced by the symbol ...
35 views

Prime-Generating Cellular Automaton

I'm trying to use these ...
313 views

Apply multiple functions to parts of a nested list [duplicate]

data = {{1, a, x, "one"}, {2, b, y, "two"}, {3, c, z, "three"}} I want to apply a list of four functions {f, g, h, m} one ...
68 views

Rule for derivatives

I have a differential equation of the form $$f'(x)=g(x,f(x))$$ (where $g$ is has a known explicit form, e.g. $x f(x)$) and I have an expression which contains several derivatives of $f$. I want to ...
74 views

Tensors constructed using KroneckerDelta's - and/or displaying KroneckerDelta as a matrix

I am doing some work in elasticity and as a result am working with tensors. In particular, I would like to calculate the contraction of a fourth order tensor (the stiffness tensor) with a second order ...
32 views

Replacing expressions with variables [closed]

I have a large matrix where the entries are rational in Jacobi elliptic functions e.g. I'd like to replace the elliptic functions by variables, e.g. ...
40 views

Generate rule that replaces if string matches pattern

I have let's say a function f[x], but for x I pass a string. And I want to replace that string with a number, if that string ...
147 views

248 views

How to set multiple parameters to zero?

Say I have the matrix A = {{a,b,c,d,e}, {f,g,h,j,k}} and I want to set some of these to zero. I have been doing this via ...
205 views

Opposite of Alternatives in a Rule

Mathematica provides Alternatives, to match one of several patterns. In a rule, this is used as p1|p2|p3:>replacement. I ...
41 views

Using Replacement Rule on Part of List? [closed]

Why can't I use a replacement rule to replace a variable name standing in for the index of a list? For example: myList={1,2,3,4,5} myList[[index]]/.index->3 ...
194 views

Executing: ...
683 views

How to replace a space by a comma

in this expression = "{1 2 3 4 5 6 7 8}", I want to replace each space by a comma , to get ...
53 views

Is there parallel/simultaneous substitution in Mathematica?

I know this is simple but I'm not proficient at Mathematica and cannot seem to find it online or in the help. Also, Replace[] says it does the assignments in order, ...
38 views

Substitution in a power transformed in product

This could be thought as a duplicate question but it's in fact an extension of an old section. 1 + (a (α + β))/(b^2 + c^2) + ((α + β)^2 a^2)/(b^2 + c^2) could ...
46 views

How to replace the argument of a function?

For the following expression, b'[x y/z]+z b''[x y/z] I want to replace the argument of b such that the above expression becomes ...
39 views

Replace argument of delayed function before it evaluates [duplicate]

How should I use replace so that f[x_] := x^2 Replace[f[3], 3 -> 1] OUT = 9 evaluates to 1, instead of 9? This way, the replacement of the argument is done ...
155 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 ...
261 views

How to program a click panel 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 ...
66 views

Find and Replace in Notebook using a Pattern [closed]

I would love to be able to use the power of Mathematica's patterns to find and replace within my code. I have searched for this on google, and so far I've come up with this: http://reference.wolfram....
131 views

How can one match a function in a replacement rule

I'm trying to write a delayed replacement rule that is capable of matching both the functions and their parameters, like ...
88 views

replacement rule doesn't work

I define a function which counts the number of negative elements in a list as follows: g[x1_, x2_] := Count[{x1, x2}, _?Negative] Plugging in values shows that ...
114 views

Replace non-zero elements with symbol

I have a very large matrix (tensor) in Mathematica with some zero and non-zero elements. I am interested in replacing the non-zero elements with some symbol or a 1 so that it is easier to view the ...
42 views

Replace higher order derivatives given lower order derivative

I have an unknown function f[x1,x2] whose partial with respect to x1 is identically zero. I would like to make sure that ...
45 views

How to define a Reduce function in order to define two parameters afterwards

I'm trying to evaluate numerically an equilibrium for a system of ODEs: dA = c A + b B - a A dB = d B + a A - b B So I define a list of known parameters: ...
41 views

Why doesn't recursive transformation stop when rules no longer match?

In an exercise where I was trying to pick out consecutive words starting with the same letter, i.e. I wanted: ...
71 views

Replace a variable with a list of numbers [closed]

How can I replace a variable with a list of numbers? Example Suppose I have the following list of values V = Table[i, {i, 1, 6.8, 0.19}]; and I want to ...
87 views

Solve equation with two different sets of replacement rules

I want to solve eqn for c0 in the following code. I want to do it with both replacement rules. I realize I could just use solve ...
230 views

What's wrong with naming a rule?

Please have a look at the code below. The second Manipulate uses the name rl of the replacement rule given in the first line, ...
240 views

How do I encode this replacement rule?

I'm pulling a 5x5 array from a larger array. The small sub-array (call it S) can contain any combination of the symbols A, B or 0. What I'd like to do is: if the array contains any matching pairs ...
463 views

What is the meaning of “/.”? [closed]

I've looked to the built-in help of Mathematica, but I still can't understand the usage of /., like in the following expression: ...
112 views

Replace list element with element from another list based on condition

I Have a list on integers and another list of "duplicates". E.g. start={{3},{1},{2},{4}}; duplicates={{1,4,7},{5,6}} I would like to substitute each element of ...
40 views

Replacement rule of pure function not working [closed]

The following code works g[x_, y_] := x^2 + y Thread[xxx[{1, 3, 4}, {10, 20, 30}]] /. xxx -> g I would like to use ...
137 views

Alternative forms to Table for iterating over replacement rules

I have a multivariate polynomial x. I get coefficients of various monomials using CoefficientRules, which returns a list of ...