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

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1
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2answers
67 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 ...
2
votes
2answers
60 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 ...
1
vote
4answers
70 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
104 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 ...
2
votes
3answers
368 views

How to manipulate nested expressions?

I have the following expression, only slightly complicated, and I'd like to do two things: Plot the elements of the lists (though messy, all are in the same ...
5
votes
2answers
87 views

ReplaceAll performance problem: packed arrays on the LHS are unpacked when the RHS is too long

The following is one of the most mysterious performance problems I encountered and came up while extending the booleval function mentioned here. I am looking for a ...
2
votes
4answers
168 views

Replacing High Densities of 1.s in Very Large Binary Arrays

I am working with very large binary arrays on the order of {100,100000}. It may look something like this. ...
3
votes
2answers
118 views

Replacing Patterns In a List of Varying Length

I am working with an array of data that may look something like this. ...
2
votes
1answer
62 views

ReplaceAll in an expression including large InterpolatingFunction

I have a large InterpolatingFunction that I'm transforming to another basis with a few simple multiplications and additions by (symbolic) constants. The ...
0
votes
1answer
46 views

What's wrong with my rule? [duplicate]

Consider a simple code to form a SparseArray: Q = 5; a = Table[i, {i, Q}]; SparseArray[{{j_} /; j > 2 -> a[[j]]}, {Q}] Part::pspec: Part specification j ...
0
votes
0answers
39 views

Hashing by Equals instead of SameQ

I have some numerical code involving complex numbers representing points on a plane. Some of these are equal but not identical, ie ...
0
votes
2answers
108 views

How to assign special colors to the output of DensityPlot?

I have created the following function for plotting ...
2
votes
2answers
141 views

Matrix exponential via Cayley-Hamilton Theorem

I'm attempting to calculate the exponential of a matrix via Cayley-Hamilton theorem. (Following the "concrete example" from http://en.wikipedia.org/wiki/Cayley%E2%80%93Hamilton_theorem) I am having ...
4
votes
1answer
235 views

Apply color function to matrix plot

I want to apply the following color rules to a large table of numbers. I have extracted a part of the table to use as an example. I would like to assign 5 different colors to 5 different ranges of ...
1
vote
1answer
68 views

How can I get the functionality of a command ReplaceAllList?

I'm trying to use ReplaceList to match subexpressions. I expected the command: ReplaceList[{p, {p, p}}, {x_, y_} -> x y] to output two results, equivalent to: ...
0
votes
2answers
88 views

Replace one order of derivative inside higher one

How could I replace for example: Derivative[2][f][x] by Derivative[1][g][x] where ...
2
votes
2answers
144 views

Create Table of replacement rules

I want to create a table of replacement rules. ...
0
votes
2answers
108 views

Why does Mathematica not replace the derivative of $theta$1'[t]?

I want to know the velocity of point $p$, given that I know the coordinate. $p_x=L_1\cos(\theta1)+L_2\cos(\theta1+\theta2)$ I calculate $\frac{dp_x}{dt}$ to achieve the velocity of point $p$ about ...
0
votes
2answers
53 views

Evaluate differentiation after replacement

The problem is Find two linearly independent solutions of $2x^2y'' -xy' + (-4 x + 1)y = 0, \, x>0$ of the form $y_1 = x^{r_1}(1 + a_1 x + a_2 x^2 + a_3 x^3 + \cdots)$ and $y_2 = x^{r_2}(1 + b_1 x ...
10
votes
1answer
215 views

StringReplace, ReplaceAll and Rule interact in a bizarre way

I have the following pair of things: ClearAll[foo, labeledFoo]; labeledFoo = {"FooBarBazQuux", foo}; This works like you'd expect: ...
4
votes
2answers
125 views

Replacing a function in defined expressions

I'm having a little trouble with substituting functions into an expression. A minimal example is as follows: ...
0
votes
1answer
77 views

Append subscript to variable name [duplicate]

I'm importing equations from Word document and transforming them into input form. But subscripts look ugly. Is is possible to programmatically append subscript to variable name? e.g. ...
1
vote
0answers
38 views

How can I use the Rules returned by FindFit? [closed]

When I evlauate data = RandomReal[10, {5, 10, 2}]; fit[i_] := FindFit[data[[i]], a Sin[x] + b, {a, b}, x] fit[1] I get something like: ...
11
votes
4answers
276 views

Replacing parts of a held expression with held parts of another expression

I'm applying the Trott-Strzebonski technique in order to replace inside a held expression. ...
0
votes
0answers
133 views

Calculating the Lyapunov Exponent/Spectrum for the Duffing Oscillator

Some fellow students and I are trying to calculate and plot the Lyapunov spectrum for the Duffing oscillator (currently a test approach). Each of us has Mathematica knowledge based purely on past ...
0
votes
2answers
119 views

How to partition three years of data into daily samples

I'm trying to find mean of temperature data list. The temperature data list has 3 hours steps which means I have 365*8=2920 temperature measurements per year. My data are temperatures of 13 years. ...
2
votes
1answer
70 views

Using Total on a list supplied by a rule

I'm confused as to why Total complains about a nonatomic expression here: ...
2
votes
1answer
59 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. ...
0
votes
1answer
103 views

Replacement rules in combination with pure functions to make a change of variables

I have defined my function in this way w = f[r,Θ] ; After some calculations i obtained my results with respect to the previous function. For instance: ...
8
votes
2answers
372 views

Using ReplaceAll on SparseArray

I'm using SparseArray in a notebook in which I am doing complex conjugation manually, i.e. writing $\sqrt{-1}$ as i and applying ...
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 ...
2
votes
1answer
77 views

Applying rules to rewrite expressions that contain patterns

I'm trying to write a rule that can rewrite a pattern that exists in another expression. For some reason, this is proving to be more challenging than I expected ... most likely because I'm not totally ...
1
vote
0answers
39 views

How to apply an rule to factors matching a certain form

Suppose we have many expressions involving irrational ArcTan expressions (such as ArcTan[Sqrt[3],5]) along with other irrational factors (such as ...
0
votes
2answers
118 views

Replace matrix with conditions

I want to replace the values of 1. in slot under the condition that the year and month in basevalue and ...
0
votes
1answer
50 views

Solve equation with two different sets of replacement rules

I want to solve eqn for c0. I want to do it with both replacement rules. I realize I could just use solve twice, once for subsCoke, and once for subsPepsi. I'm trying to do it in just one Sovle to ...
1
vote
1answer
50 views

Commutative algebra by generators and quadratic relations

My apologies if this has been asked before. Please also be gentle, as this is my first question here. I am trying to define a commutative algebra by generators and relations in the following way. ...
0
votes
0answers
32 views

Block, With, Module, can anyone help me understand the distinction? [duplicate]

I've been working heavily with Block[] for months in my research so I've read the documentation for the seemingly similar commands With[], Block[], and Module[]. Personally, I've had by far the ...
12
votes
7answers
2k views

How do I replace a variable in a polynomial?

How do I substitue z^2->x in the following polynomial z^4+z^2+4? z^4+z^2+4 /. z^2->x ...
1
vote
2answers
91 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 ...
2
votes
2answers
132 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 ...
1
vote
3answers
155 views

Conditional Check on Matrix

Suppose I have the following matrix (i,j): ...
0
votes
0answers
79 views

Back Linear Substitution

I have an equation set Ax=b and A(n*m),n<m . To lower down the dimension, I express some vars by other vars, which gives ...
0
votes
0answers
19 views

Manipulating named patterns inside replacement rules [duplicate]

When I evaluate the following expression, {a -> "value1", b -> "value22"} /. {Rule[x_, y_] -> Rule[x, y]} I get ...
3
votes
0answers
64 views

Why doesn't ReplaceAll work on Image? [duplicate]

ReplaceAll seems not to reach inside Image, and I don't see why it shouldn't. Here is an example. Create a black and white image ...
1
vote
2answers
133 views

Replace a column in table with a list of numbers?

I have a Table of values e.g. {{x,y,z},{x,y,z},{x,y,z}…} How do I replace the the "z" column with a List of values?
4
votes
1answer
191 views

replace items in a list with items in a another list

Suppose I have a list A={x1,x2,x3}, a list B={3,4,5}, and a function f[x]=x1+x2+x3. Is there ...
1
vote
2answers
88 views

How to “reversely” replace definitions?

I have the following problem at hand. 1.) I have a list of definitions like ...
5
votes
5answers
1k views

Replace values which obey certain criteria

I'd like to replace all values in a list which obey one or more criteria with another value. Example: Replace all values>30 by 30. data={{3,35},{2,7}} ...