Total¶

Sums the elements of a list.

$ wo 'Total[{1, 2, 3}]'
6

A level-0 spec leaves the expression untouched:

$ wo 'Total[{{1, 2}, {3, 4}}, {0}]'
{{1, 2}, {3, 4}}

An empty list totals to 0 at every positive level:

$ wo 'Total[{}, {2}]'
0

A trailing option is not a level spec, so it leaves the total alone:

$ wo 'Total[{1, 2, 3}, Method -> Automatic]'
6

By default only List is descended through, so another head is left as it is:

$ wo 'Total[f[1, 2, 3]]'
Total[f[1, 2, 3]]

AllowedHeads -> All descends through any head:

$ wo 'Total[f[1, 2, 3], AllowedHeads -> All]'
6

$ wo 'Total[{1, f[2, 3]}, 2, AllowedHeads -> All]'
6

Only as deep as the level asks, and an exact level keeps the head above it:

$ wo 'Total[f[1, g[2, 3]], AllowedHeads -> All]'
1 + g[2, 3]

$ wo 'Total[f[1, g[2, 3]], {2}, AllowedHeads -> All]'
f[1, 5]

Rationals and complex numbers stay atoms however permissive the heads are:

$ wo 'Total[{1/2, 1/3}, AllowedHeads -> All]'
5/6