Questions about how Mathematica evaluates expressions, tracing evaluation (Trace*), handling expressions in unevaluated form (Hold*, Unevaluated), nonstandard evaluation, etc.

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5
votes
1answer
155 views

Force Dispatch to generate dispatch tables

Dispatch creates hash tables only for lists of length larger than 3. Is there any way to force MMA to create hash tables even for lists of length smaller than 4? ...
5
votes
4answers
119 views

How to map Unevaluated over a list

I have a list {a1, a2, ...... , an}, in which all as have been initialized to a number. I want to get: ...
4
votes
2answers
164 views

When are numerical expressions identical

Very elementary: 2 + 3 == 5 evaluates to True and 5 == 5 evaluates to ...
2
votes
0answers
43 views

Find the numerator of 6/8 [duplicate]

The statement Numerator[6/8] evaluates to 3. Numerator[Hold[6/8] does not work. What function NewNumerator[6/8] evaluates to 6?
6
votes
1answer
94 views

Debugging a $RecursionLimit error?

I sometimes encounter bugs that involve a recursion limit. It's often very hard to find the origin of the problem. Would there be a way to copy the stack somewhere and abort the evaluation in order ...
16
votes
1answer
374 views

Quit the Kernel and start new session automatically

The question is how to quit the kernel, start a new session automatically, and to be able to run such procedure from e.g. Button. This is especially useful when ...
2
votes
2answers
74 views

Evaluation speed of apparently equivalent functions

Consider the following expressions: f[x_Integer] := x, f[x_] := x /; x ∈ Integers, f[x_?IntegerQ] := x All of the expressions above (and probably others which ...
4
votes
2answers
49 views

How to print unevaluated arguments in the form they were originally typed in?

I'm looking for a way to print a function's arguments, not only unevaluated, but also in the way they were originally typed in. By way of experimentation, I tried stuff like this: ...
1
vote
1answer
40 views

How to get Mathematica to abort the current evaluation if an assertion fails?

I can turn on assertions, but they don't terminate the current evaluation. For example: ...
7
votes
5answers
209 views

Generate list of strings from a list of assigned variables

How do I generate a list of strings from a list of assigned variables? Eg. Convert ...
8
votes
3answers
233 views

Graphics in Notebook Different from Graphics Expression?

Consider the expression TreeForm[a+b^2+c^3+d] which displays as This is a nice Graphics object, as I can prove by typing ...
75
votes
5answers
48k views

Get a “step-by-step” evaluation in Mathematica

Is it possible in Mathematica to get a step-by-step evaluation of some functions; that's to say, outputting not only the result but all the stages that have led to it? If so, how does one do it? ...
1
vote
1answer
46 views

GCD of Table entries

This question is from a newbie, so please be gentle in thrashing if I'm missing something very basic. How can I use GCD on a matrix/vector entries stored as Table. For example, if ...
20
votes
5answers
955 views

How do you programatically load data into symbols?

I am trying to convert a list of string names into symbols, which will then be used to store data. I have 24 files (where the name of each file is a member of the list mentioned above) that I need to ...
0
votes
0answers
31 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: ...
2
votes
1answer
60 views

Why isn't Table iterator value inserted in failed NIntegrate arguments?

Consider this simplest example: Table[{z, NIntegrate[f[x], {x, 0, z}]}, {z, {1}}] Here f is not defined, so ...
5
votes
0answers
154 views

Built-in symbols which are more close to the root/core of Wolfram Language

Seeing the vast scope of science covered by the Wolfram Language (WL) and the large amount of built-in symbols (functions), I am curious to know which built-in symbols are more close to the root of ...
0
votes
0answers
26 views

What makes items with head `Function` different?

I apologize beforehand for the muddleheadedness of this question. It reflects the fact that I'm trying to interpret outward "behaviors" of Mathematica expressions without having any understanding of ...
0
votes
0answers
23 views

Timing of an Evaluation is not correctly displayed

From: http://reference.wolfram.com/language/howto/DisplayTheTimingOfAnEvaluationInANotebookWindow.html I ran a process that took about two minutes to finish. But the time recorded is only 0.18 ...
1
vote
1answer
51 views
0
votes
1answer
60 views

How do you stop Mathematica from evaluating a sum? [closed]

A concentration $A(i,j)$ varies over i,j. I'd like to include the summation of $A(i,j)$ in my Mathematica expressions, but it evaluates the sum ...
0
votes
0answers
65 views

Creating a lazy evaluator of the lambda calculus

I have a sub project in my research to write a lazy evaluator of the lambda calculus. How should I approach this problem? I already have a implementation of the lambda calculus in another language. ...
1
vote
0answers
41 views

Unexpected order of evaluation in ForAll

I noticed that ForAll behaves rather unexpectedly when its first argument is a symbol which has been Set in an outer scope. For ...
4
votes
0answers
110 views

Why the flat f[x] is treated as ghostHead_[f[x]]?

While reading this answer I feel confused. If we do not care any specific detail of the original question, then ybeltukov's answer essentially makes use of the following fact ...
3
votes
1answer
226 views

Output an Expression in terms of GoldenRatio

Sorry if this is a dumb question (I'm new). I swear I searched and read forums first! I'm trying to rewrite expressions in terms of the Golden Ratio. For example, I know 9+4Sqrt[5] is Phi^6, but can ...
-2
votes
1answer
113 views

Why does Mathematica “sleep” when I don't work at computer? [closed]

I started using Mathematica few days ago. I'm running this code: ...
1
vote
1answer
47 views

Replace symbols in output without evaluation

I found the Wolfram example for ExpandNCM but I want a more human-readable output form. I want to evaluate ExpandNCM, for example with ...
-1
votes
1answer
127 views

need help to price a european option using finite difference method [closed]

I am writing a function to price European option using backward induction finite difference method. The function is expected to price a European option taking Stock (stock_), age (time_), volatility ...
4
votes
2answers
125 views

Coarse-graining in numerical integrations

I have been working recently in a coarse-graining problem I found when using NIntegrate: I am trying to evaluate the function $$f(a)=\int_0^{\infty}x\,e^{-(a^2+b^2)x^2}\text{d}x$$ numerically as a ...
3
votes
1answer
104 views

Evaluation of Derivative in a Module

Can someone help me understand the evaluation procedure in the following two pieces of code? ...
2
votes
0answers
63 views

What is the difference between GenerateDocument and TemplateApply[NotebookTemplate[

Abstract GenerateDocument[ _NotebookObject ] seems to do the same what TemplateApply[ NotebookTemplate @ _NotebookObject ] ...
1
vote
2answers
56 views

Evaluating and Plotting Multiple Zero-Counting Functions

In work that I am doing, I am trying to plot multiple zero-counting functions, depending on how a parameter works. For example, if the zeros of one function are {1, 2, 3, 4, 5, 6, 7}, the zeros of ...
16
votes
4answers
355 views

Result about Context is inconsistent with the description of “Power Programming with Mathematica”

x = 5; temp`x = 6; Begin["temp`"] {x, Global`x, temp`x} The result in my Mathematica session is {5,5,6}, but it's ...
0
votes
2answers
42 views

Different behaviour of Map and Inner in replace rules

Why does x[{1, 2}] /. {x[l_] -> Map[func, l]} {1, 2} not behave as expected, while for example ...
1
vote
1answer
72 views

How to Reap data from a ScheduledTask?

Here is an amusing little function mapped over a range just to iterate it. It ignores its argument and works entirely by side-effecting a global variable: ...
14
votes
1answer
435 views

What is the real default CellEvaluationFunction?

The default CellEvaluationFunction is Identity but one can quickly see that this is handled specially as an equivalent function, ...
1
vote
0answers
87 views

How can I use L.Shifrin s code formatter package better

in the document of HoldAllComplete, it says: Evaluate cannot be used to override HoldAllComplete.. for example, when I'm ...
0
votes
2answers
43 views

Expand “hierarchical” system of equations

I have a system for equations that is structured hierarchically: - Level 0: these are base variables that I can measure from a process (e.g. a,b,c) - Level 1: these are variables derived from Level 0 ...
0
votes
1answer
65 views

Why does Compile redo the calculation when overflow happens?

When implementing the Numerov method solving Schrodinger equation, I encountered this problem. In order to show the order of the evaluation, Print is added. ...
5
votes
1answer
169 views

How is LHS = RHS; … ; RHS (nontrivially) different from … ; RHS

I'm trying to understand how Mathematica thinks about the results of Set. Suppose we perform LHS = RHS. I'm focusing on when ...
0
votes
0answers
31 views

Alter evaluation order when applying scalar multiplication to function

Consider the following program: g = 2f; g[x] (* (2f)[x] *) Is there any way I can change the above expression to have it return ...
2
votes
1answer
172 views

Is there a way to simplify a symbolic expression at assignment, once-for-all?

I have a series of symbolic function calls that could be greatly simplified using some assumptions. I think I would like for these assumptions to be used in the definition of the function so that they ...
2
votes
1answer
100 views

What is “ (Dialog) Input [ ] := ” after evaluating a cell?

I have done a time-consuming run and calculation. After many hours ( about 7 hours!), the black color which shows that the cell is evaluating, turn into gray and a strange text appears like this : ...
27
votes
2answers
2k views

What are the cool kids talking about when they use ##&[]? [duplicate]

All the cool kids are apparently using ##&[] for Unevaluated @ Sequence[] but I have no idea what either means. ...
3
votes
2answers
51 views

Simplify with assumption of unknown function [duplicate]

I have an unknown multivariate function entry[x,y,z], which is positive. Then how to get FALSE and entry[1,2,3] in the following evaluations? ...
13
votes
5answers
1k views

How are parameters evaluated for a Plot in Manipulate

I am trying to get my head around how Manipulate evaluates functions in a Plot. I have read the introduction to Manipulate, and introduction to Dynamic, but I still ...
11
votes
3answers
5k views

General::ivar is not a valid variable when plotting - what actually causes this and how to avoid it?

I was just evaluating a couple of expressions and started to get errors like this: ...
2
votes
1answer
114 views

Nested If statement with unevaluated arguments

I have a list of boolean functions {f1, f2, f3, ...} that take a value and return True or ...