What is ___ vs _ in Mathematica ?

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In summary, "lis_list" means that the variable "lis" can only match a list in the Mathematica declaration "myfunc[lis_list]". Additionally, the symbols "_" and "__" represent patterns that can match any single expression or sequence of expressions, respectively. It is recommended to consult Mathematica's help system for more information on pattern matching.
  • #1
Physics_rocks
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0
Hi guys ,

I have the next declaration in Mathematica :

myfunc [lis_list]

and myfync [x_,y___]

what does "lis_list" means ? I know that when I want to declare a variable of a function
I must write myfunc[SomeVar_] with one _
but what are 3 times _ (meaning ___)

I hope I'm no asking a stupid question :)

thanks !
 
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  • #2
I don't think it does anything? Testing it, it seems to have no effect.
 
  • #3
_ is a pattern which can stand for any single expression, whereas ___ is a pattern that can stand for any sequence of 0 or more expressions. There is also __ which is a pattern that can stand for any sequence of 1 or more expressions.
 
  • #4
Physics_rocks said:
what does "lis_list" means ?
It means that "lis" is only allowed to match a list, methinks. Mathematica's help system has a section on pattern matching -- it might be useful to go read it.
 

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