Piecewise

Piecewise({{expr1, cond1}, ...})

represents a piecewise function.

Piecewise({{expr1, cond1}, ...}, expr)

represents a piecewise function with default expr.

See:

>> Piecewise({{-x, x<0}, {x, x>=0}})/.{{x->-3}, {x->-1/3}, {x->0}, {x->1/2}, {x->5}}
{3,1/3,0,1/2,5}

Heaviside function

>> Piecewise({{0, x <= 0}}, 1)
Piecewise({{0, x <= 0}}, 1)

Piecewise defaults to 0, if no other case is matching.

>> Piecewise({{1, False}})
0

>> Piecewise({{0 ^ 0, False}}, -1)
-1