Questions tagged [pattern-matching]
Questions on expression testing and manipulation through pattern matching and constructing efficient patterns.
1,615 questions
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What is the meaning/utility of __[] AKA BlankSequence[][]?
I understand BlankSequence in other contexts, but not this one __h means a pattern of one or more things each of which have head ...
- 1,606
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What, if any, is the list analogue of KeyValuePattern?
I am trying to understand the function of KeyValuePattern. According to the documentation,
KeyValuePattern[{patt1, ...}] is a ...
- 10.6k
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Matching an expression in Hold
Trying to replace some of the expressions wrapped by Hold as below to get $\frac{k d\theta }{dt}$, ReplaceAll does not replacing ...
- 1,484
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Replacement of I to -I not working [duplicate]
Let
$f(x) = A \exp(i k x) + B \exp (-i k x)$.
If we replace every $i$ by $-i$, we are supposed to get
$g(x) = A \exp(-i k x) + B \exp (i k x)$.
However, the Mathematica code does not work as expected.
...
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Why is Position with level spec {1} evaluating on {0}?
The title says it all. These two examples both have StringEndsQ emit an error message because it's being evaluated on the head of the input list.
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- 4,293
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Using Switch to return a value depending on the sign of a real number
I would like to use Switch to test if a real number myNum is negative, zero, or positive and to return "N", "Z&...
- 10.6k
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How to define the derivative of variables inside an expression so chain rule can be correctly applied to the full expression
I don't use Mathematica as much and only use it for some specific tasks from time to time (mostly simplifying expressions and calculating integrals and derivatives).
Lets say I have an large ...
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How do we find an asymptotic approximation of the function $\mathbf{P}(r)=\left(t_1+\prod\limits_{k=1}^{r}(t_2+k^{s})\right)^n$?
Suppose we have the following function, where $s\in\mathbb{R}$ and $t_1,t_2,n\in\mathbb{N}\cup\{0\}$ are constants:
$$\mathbf{P}(r)=\left(t_1+\prod_{k=1}^{r}(t_2+k^{s})\right)^n$$
Question: What is ...
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Finding full-depth positions ("absolute positions") of elements within sublists satisfying a criterion
I have exampleList, a list of lists of lists:
...
- 10.6k
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What's happening when we execute a_b=1?
OK, of course I know that, as mentioned in e.g. here, symbol names in Mathematica cannot contain underscore _ because it's a reserved character, but, what's ...
- 71.6k
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Usage of replacement
With a naive thought, it seems that rule as below can match in expr. However, it does not match. Could I know what mistake I ...
- 1,484
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Why f[x___] := {x==="To be", x=!="not to be"} is both True for f[]?
The behavior of pattern matching in functions surprised me at the
unexpected behavior of this example
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- 5,252
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Why does MatchQ[ 3 + x, _ + _ ] return False?
Consider
MatchQ[ 3 + x, _ + _ ]
It returns False. Why?
After some research, I concluded that it's due to the ...
- 183
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Difference in pattern matching before & after Expand
The goal is to substitute m2/m1 in expr with k. Code1 does not match the pattern, but if it is pre-processed with Expand like in code2, it matches the pattern. Could I know why there is this ...
- 1,484
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Unexpected result with Position using pattern
I use Mathematica 12 and have the following code
t1 = {1, 2, 3.1, 4, 5, 6, 7.1}
Position[t1, x_ /; Not[IntegerQ[x]]]
which gives me
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- 3,150