Aron Y. answered • 08/17/19
Used Mathematica extensively since 2003, for scientific and genl. work
It's shorthand notation for Apply. [Specifically, within Wolfram Language, this is considered "Prefix"-style notion]. So:
test ={a, b, c, d};
Apply[Plus, test]
>> a + b + c + d
Plus@@[test]
>> a + b + c + d
I.e., Plus@@[test], and Apply[Plus, test], both mean "Apply the function Plus to the List named test".
It's useful to distinguish Apply and Map (/@). Consider some function f. Then:
Apply[f, test]
>> f[a, b, c, d]
f@@ test
>> f[a, b, c, d]
Map[f, test]
>> {f[a], f[b], f[c], f[d]}
f/@test
>> {f[a], f[b], f[c], f[d]}
As a reasonable simplification, Apply applies a function to the list as a whole, while Map applies a function to each individual element of a list.
