70 questions linked to/from Replacement inside held expression
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### 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: ...
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### 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
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### 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 ...
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### Evaluate part inside HoldForm [duplicate]

What I want to do is pretty straight forward: Entere something like this: HoldForm[Sum[la /. a -> b, {l, 0, N}]] and get something like this Σ lb Generally spoken, holding the sum but evaluating ...
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### ToString with delayed replacement [duplicate]

I want a toString method that replaces each occurrence of f[x_]. ...
• 1,093
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### 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 ...
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### 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 ...
• 8,666
157k 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 ...
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### 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 <...
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### 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?
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### 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 ...
• 1,069
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### 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, ...
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### 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. ...
• 3,686
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### Does Set vs. SetDelayed have any effect after the definition was done?

I was always assuming that the only difference between Set (=) and SetDelayed (...
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