Questions tagged [downvalues]
Questions about DownValues which specify function definitions for symbols.
14
votes
3answers
200 views
What is the difference between Set and SetDelayed when evaluating the RHS leaves it unchanged?
I thought there was no difference between f[a_] = 2 + a; and f[a_] := 2 + a; because the resulting ...
2
votes
2answers
55 views
Correct way to see domain of function using DownValues?
Here's a simple function g defined for the natural numbers 1 through 10:
Table[g[i] = i^2, {i, 1, 10}]
I now want to find the ...
0
votes
1answer
35 views
Cannot set DownValues to ValueList while loading package
I have installed a package named HEP from Wolfram Library Archive which contains several .m files by Files -> Install (...
6
votes
2answers
191 views
What makes a pattern more general?
This is a rewording of the question. The original post is below.
How come that a pattern for an expression with a specific head is not more specific than a pattern for an expression with a generic ...
1
vote
0answers
34 views
Pure OwnValue Functions vs Patterned DownValue Functions [duplicate]
Is it better to use pure Function assigned to symbols as their OwnValues vs function defined by patterns as symbol's ...
2
votes
2answers
42 views
Defining a property of a variable that includes another function (sign)
I have a function that has a lot of sign functions that depend on a variable $\sigma$ and I know the property that $\sigma=1$ with probability $m$ and $-1$ with probability $1-m$. For example we can ...
2
votes
0answers
41 views
How to add sugar for NetEncoder?
I'm tired of the extra level of list in NetEncoder and would like to get rid of it.
The obvious thing fails:
...
10
votes
2answers
173 views
Unexpected behavior when directly assigning to DownValues
I'm encountering some unexpected behavior when assigning to DownValues. When I assign two definitions for test[1] as below, ...
4
votes
1answer
126 views
Sorting a list of rules
When we give several definitions for a function f, the DownValues of f are automatically ...
4
votes
2answers
212 views
Wrongly assigning a value to an expression
Sometimes I misstype an equality and I write an assignment instead.
For example, if I write
f'[x] = 2
instead of an equation, ...
1
vote
1answer
67 views
Changing DownValues of a function when calling
General problem
I am looking for a possibility to store information in parallel for a function and change the information when a function is called.
Idea
It seems possible to solve this problem by ...
7
votes
1answer
191 views
Why can I define N[MySymbol] := …?
As far as I understand, I cannot define the values of built-in functions: Sin[Cat] := Dog will result in error.
This is because all built-in symbols have attribute <...
5
votes
1answer
537 views
Optimize DownValues: extract “non-patterns” from Alternatives
Introduction
As we know, when we assign DownValues to a symbol, Mathematica creates a dispatch table for "non-pattern" definitions (i.e. expressions that, when ...
4
votes
2answers
91 views
Assigning values to association in DownValues
Compare the following code:
Clear[t];
t = <||>;
t[2] = 1/2;
t[2]
with
...
2
votes
2answers
94 views
Memoization and finding already calculated DownValue
The problem of plotting an expensive function discussed in this question caught my attention. As an exercies I tried to solve it using memoization as follows
...
8
votes
0answers
141 views
KeyValuePattern specificity in DownValues
Bug introduced in 10.4.0 and persisting through 11.3.0
CASE:3824590
[...] Developers are discussing this behavior. [...] I will let you know when I have definite information on this. [...]
...
0
votes
1answer
58 views
Trying to “fix” Simplify, but cannot Up/DownValue it because it is Protected
There is an irksome shortcoming for Simplify that I encountered:
Simplify not evaluating completely with Square roots
-- still not entirely sure if it's because of AssumptionsMaxNonlinearVariables ...
3
votes
1answer
262 views
How to “clear” the downvalues of a subscripted variable?
I have a function that sets certain subscripts of the symbol aa as in the following example:
...
0
votes
3answers
319 views
How to initialize downvalues from a list?
The For expression below initializes downvalues of a variable a from the values in a list ...
4
votes
1answer
63 views
Using ValueQ to test whether “hash” key exists fails when key is given as variable
Please ignore ^^^ possible duplicate (raised by me). The solution doesn't cover my case.
I'm trying to implement a simple hash table according to this top answer at "Is there HashTable structure in ...
1
vote
1answer
82 views
How to extract all necessarily code for a function?
Many times when someone pastes a piece of code into SE there are missing values and symbols that the user left out.
To prevent this I'm looking for a function that uproots other functions (extract ...
10
votes
6answers
376 views
Combinations of multiple matching patterns
I wonder if there is any nice way to combine DownValues (or any other suitable rule-/pattern-/function -based Mathematica construct) when multiple patterns match an expression. Let me explain what I ...
4
votes
2answers
1k views
How to take derivative of a interpolated function inside the module
When handling derivatives of a interpolated function, I often use the following function
makeDeriv[f_InterpolatingFunction] = D[ f[x], x]
Then, I can define ...
14
votes
2answers
377 views
Named patterns in Except
Bug introduced in 8 or earlier and fixed in 10.4.0
Bug isn't present in version 5.2
I don't think I quite understand how Except works.
I want to define $f(a,b) = ...
28
votes
5answers
1k views
What are the requirements for a well behaved indexed variable? Subscript, ToExpression, Downvalue?
On writing this answer I needed to call a function, (NonlinearModelFit) with an unknown number of parameters.
We have learned that we should not use ...
12
votes
1answer
125 views
Which symbol gets DownValues or OwnValues when using SetDelayed?
I have been looking at various usages of Pattern objects. Here's a number of ways to define the same thing:
mod[x_] := {x}
...
0
votes
0answers
35 views
Why is DownValues releasing RuleDelayed's hold for Graphics? [duplicate]
I am trying to understand DownValues in regards to the evaluation of its output. Consider this:
...
5
votes
1answer
197 views
Multiple down-values with exactly the same lefthand side
I was working on an answer to this question, when I was sidetracked by what I bring up here.
I wanted a function, which when given a string representing a binary number, would convert the string to a ...
5
votes
3answers
3k views
How to force 2+2=5
I was looking at this question (writing a program such that 2 + 2 = 5) and tried to write something in Mathematica, but I couldn't get something to work without completely replacing ...
4
votes
4answers
437 views
How to do memoization together with evaluation of a complicated function
UPDATE 2: much shorter version
Given a list of paired indices {i, j}={{1,2}, {3,4}, …}, I need to first evaluate a rather complicated function test[i,j,x] (because ...
2
votes
1answer
157 views
How do I constrain movement for lists of Locators using 2nd argument of Dynamic?
I need to display edge labels of a graph in a way that allows the edge labels to be moved. Locator seems the simplest and most obvious function to use. My ...
2
votes
0answers
87 views
Function that assigns properties [duplicate]
I want to create a function that creates and assigns properties to a symbol. In theory this would behave similarly to the NonzeroValues property of ...
3
votes
1answer
321 views
String pattern matching in function definition [duplicate]
I have a function f and its downvalues. I want to code an extra downvalue for arguments of the form "part1:part2"
I don't understand why
f[a__~~":"~~b__] := {a,b}
...
7
votes
1answer
191 views
Graphics Function Definition Style (Using SubValues vs. DownValues)
I am going through some of the items in "Modern Differential Geometry of Curves and Surfaces with Mathematica, Third Edition".
An example of the style used by these authors is:
...
6
votes
1answer
276 views
How can I define a ⊕ operator?
What is wrong with the following code?
CirclePlus := SparseArray[Band[{1, 1}] -> {##}] &
a_ ⊕ b_ := CirclePlus[a, b]
SetDelayed::write: Tag Function in (...
2
votes
2answers
323 views
How to unprotect GeneratingFunction
I'm trying to add custom downvalues for GeneratingFunction, and to do so I thought I just had to Unprotect it. However, that ...
4
votes
0answers
172 views
DownValues for Built-in Functions
N.B. I have bitten the bullet, and I am going through Leonid Shifrin's "Mathematica Programming: An Advanced Introduction." (Which needs no introduction in this forum)
One question I have: could one ...
4
votes
2answers
546 views
Overloading conjugate operator for a particular function
I trying to modify the behaviour of the built-in Conjugate[] operator on a particular function I have defined, to take into account that some of its variables are ...
1
vote
2answers
202 views
Given a list of date and value pairs, efficiently sum the values by date [duplicate]
I have a list of date & value pairs. There can be multiple entries for each day. Sample data can be generated with the following:
...
9
votes
1answer
260 views
Unset variable by its name given as a string
Unlike the function Clear, the function Unset does not work for string patterns. Given the name of a variable as a string, how can you unset the corresponding variable? Example:
Given:
...
5
votes
2answers
451 views
DownValue “associative array” to list? [duplicate]
I have a "sparse array" like this
arr[1.5]=0.4, arr[3.5]=0.7, arr[7]=0.3
which is not really a sparse array since the keys are not all integers. This is like a ...
4
votes
1answer
186 views
Downvalues vs. Scoping for Functions
Regarding my recent question on using a default value for a function argument when a pattern was not met yielded some interesting answers, but the general consensus was "Yes this can be done, but ...
5
votes
2answers
176 views
Get DownValues that do not involve patterns?
Say I have a function with a few definitions that also implements memoization:
f[x_] := f[x] = x^2
f[x_, y_] := f[x, y] = x^2 + y^2
I then apply the function to ...
9
votes
2answers
983 views
How to get the list of defined values for an indexed variable?
I would like a table with rational indexes - thus it would be practical to use a dictionary, which, in Mathematica are implemented with the indexed variables. I would like to be able to do:
...
49
votes
3answers
2k views
How is pattern specificity decided?
Mathematica has a notion of pattern specificity, which is a partial ordering on patterns.
The rules (e.g. DownValues, SubValues,...
2
votes
0answers
146 views
How safe are ReadProtected and Locked symbols? [duplicate]
Possible Duplicate:
How to distribute proprietary Mathematica code
I suspect that there is a way to expose the down values of such symbols with an attack along these lines:
...
14
votes
1answer
493 views
Selectively clear DownValues
How can I clear a subset of a symbol's DownValues ?
For example, suppose I have created some DownValues for $f$ like this:
...
20
votes
5answers
6k views
The difference between 0. and 0
I have a function for which 0 is a special case:
f[A___, 0, B___] := 0
But since I am doing numerics, sometimes in the course ...
6
votes
3answers
206 views
Organizing similar datasets using DownValues instead of Contexts
In his answer to this question, Leonid helped me find a way to programmatically generate contexts for holding sets of symbols with the same names. Perhaps a simpler way is to use ...
