Linked Questions

22
votes
2answers
1k views

How to inject an evaluated expression into a held expression? [duplicate]

I know that there are methods to structurally manipulate held expressions (discussed e.g. here), but I failed to apply those for this particular problem: ...
2
votes
1answer
890 views

How to evaluate some parts of an expression inside Hold? [duplicate]

I want to return a Hold expression but with some parts pre-evaluated. The easiest way to explain this is probably through code example. Here is what I have ...
1
vote
0answers
119 views

How to substitute inside Hold? How to create table of summation (with Sigma symbol) expressions? [duplicate]

I would like to create table of summation expressions, which are not evaluated, but summation limits are substituted. I can't accomplish this so far. If I write I get summation expanded. If I ...
2
votes
0answers
53 views

Purpose of construct `With[{var=myComputation[…]}, var/;True]`? [duplicate]

Could someone please give an illustrative example showing the purpose of construct of form With[{var=myComputation[...]}, var/;True]? Also, I wonder what kind of ...
3
votes
0answers
48 views

How does the code idiom for replacing part of a held expression work? [duplicate]

I've seen this idiom used in different programs but never fully understand why it is necessary. Could someone explain? Is it still the recommended way to replace some part of a held expression to its ...
521
votes
19answers
129k views

Where can I find examples of good Mathematica programming practice?

I consider myself a pretty good Mathematica programmer, but I'm always looking out for ways to either improve my way of doing things in Mathematica, or to see if there's something nifty that I haven't ...
8
votes
7answers
1k views

How to display very small numbers in Mathematica?

I am trying to evaluate the function: $$f(x) = \cos(x) - \mathrm{e}^{-2.7 x}$$ at $x = 1.7 \times 10^{-25}$ and Mathematica keeps returning '0.' How do I evaluate the expression in a better way?
41
votes
2answers
2k views

What are all the “magic” Symbols in the Mathematica language?

Leonid Shifrin once wrote (excerpted): (Unevaluated) is one of a very few "magic symbols", along with Sequence and ...
17
votes
5answers
591 views

Is it possible to construct a fullform trace function

Is it possible to construct a FullFormTrace function that takes an arbitrary expression and prints a sequence (or returns a list) of the evaluation steps in full ...
19
votes
3answers
832 views

Generating assignments and transforming code inside held forms when generating code

I have been playing with slightly above trivial code manipulations in Mathematica. I thought Mathematica would be great for this kind of work because of rule replacement and expression manipulation, ...
17
votes
4answers
521 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. ...
21
votes
2answers
1k views

Does Set vs. SetDelayed have any effect after the definition was done?

I was always assuming that the only difference between Set (=) and SetDelayed (...
8
votes
4answers
273 views

Hold expression with RandomInteger

One more question for today: I'm trying to show two random integers with a plus (+) sign between them, in an unevaluated form. I know how Hold and HoldForm work, but they hold everything, including ...
12
votes
4answers
297 views

Is it possible to separately call the default value of a variable which isn't at the end of the sequence?

After reading this post I recalled an old question I once met. We know that we can set default values for variables of a function: ...
19
votes
1answer
908 views

Is this a bug in Replace?

Consider the following minimal examples. This one works as expected, replacing trees starting from the inside with a numerical value. ...

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