Tagged Questions

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

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1
vote
1answer
37 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 ...
26
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 ...
1
vote
4answers
114 views

Replacing more than one element from a Sublist

The following expression allows me to extract the value of x and y: ...
0
votes
1answer
38 views

Replace all instances of Integrate by NIntegrate and add a Method option

I have an analytic expression which involves several integrals Integrate[f[x], {x, lb, ub}] where the functions f and bounds ...
3
votes
3answers
153 views

Multivariate Polynomial Manipulation

I have a large homogenous multivariate polynomial in, say, 5 variables $a,b,c,d,e$. As an example take the polynomial $$a^4+2abcd+a^2 b^2+e^4+cde^2.$$ Now I would like to replace $k$-th power of any ...
2
votes
1answer
97 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
3answers
167 views

What is the order of faces on a D20? How can I optimize the order of faces on a D-n?

I am creating a customizable D20 for 3D printing using OpenSCAD, with the following code: ...
5
votes
2answers
155 views

How to make Missing[] invariant for some functions without redefining them

Missing[...] "is a symbolic object, with no default evaluation rules defined." Missing data can be tagged and enables use of filters like DeleteMissing. So it's worthwhile to normalize various types ...
10
votes
2answers
158 views

Dispatch displays rules incorrectly and evaluates when displaying

Consider this a = 3; disp = Dispatch[Unevaluated[{a -> 2}]] We see the rule 3 -> 2, rather than ...
8
votes
1answer
272 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 ...
2
votes
3answers
165 views

Simplify system functions

Consider the code defining two constants: a=Cos[t] b=Sin[t] Suppose that we have another value in terms of Cos[t] and ...
9
votes
1answer
70 views

Using PatternSequence on its own in ReplaceAll?

Say I have this list: list = {0, 1, 2, 0, 1, 3, 0, 1, 4} and say I want to remove consecutive sequences of 0 and 1. I'd normally go for this: ...
11
votes
3answers
215 views

Equivalent of ReplaceAll for Associations?

Is there a nice (built-in) way to apply Replace-style rules to key-value pairs in an association? Something like ...
1
vote
4answers
188 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 ...
8
votes
8answers
863 views

How can a power of 0 or 1 be replaced?

Consider this given example for ReplaceAll 1 + x^2 + x^4 /. x^p_ -> f[p] This returns ...
0
votes
2answers
99 views

how can tangent half angle substitution be done in Mathematica?

Is it possible to replace sine and cosine in terms of tangent half-angles and again the tangent half-angles by a variable say t?
2
votes
2answers
117 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
1answer
85 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 ...
2
votes
1answer
79 views

Table with some editable cells

I have a table: I want it to be editable only where the zeros appear. I read this post Generating an editable table that can be used as input because it's almost exactly what I want, but I couln't ...
4
votes
2answers
142 views

Replacing one element of list

I have a list of sequences of x's and y's. I want to switch the last position to the "opposite" symbol - if ...
1
vote
2answers
70 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
4answers
74 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 + ...
2
votes
2answers
65 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
1answer
109 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 ...
5
votes
2answers
105 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
172 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
120 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
75 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
48 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
41 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
116 views

How to assign special colors to the output of DensityPlot?

I have created the following function for plotting ...
2
votes
2answers
164 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 ...
2
votes
2answers
157 views

Create Table of replacement rules

I want to create a table of replacement rules. ...
0
votes
2answers
120 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
55 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 ...
5
votes
1answer
306 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 ...
10
votes
1answer
228 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: ...
0
votes
1answer
100 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. ...
0
votes
1answer
76 views

How can I represent this automorphism of Q(i,a)?

Let $a$ represent some real irrational number. I am trying to perform computations with an automorphism $f:\mathbb{Q}(i,a)\to\mathbb{Q}(i,a)$ which fixes $\mathbb{Q}(i)$ pointwise and maps $a$ to $i ...
4
votes
2answers
131 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: ...
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: ...
0
votes
0answers
154 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
120 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
77 views

Using Total on a list supplied by a rule

I'm confused as to why Total complains about a nonatomic expression here: ...
1
vote
1answer
69 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
1answer
103 views

Replacing powers of $n$-th partial sums in the output of a function with $S[i]$ for $i = 1,\ldots,n$

I've written some simple code that, for various $N \geq 1$ and $k = 1,\ldots,N+1$ computes the $n$-th derivative of $\log S_N$ where $S_N(z) = \sum_{k=0}^N \frac{1}{k!}z^k$ as follows: ...
2
votes
1answer
69 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
114 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: ...
3
votes
1answer
210 views
1
vote
1answer
111 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 ...