The heaviside function is the step function,

By default, heaviside(x) will evaluate only when the result is an exact value, or when the input x is a floating point number.  When x is a symbolic expression, it will remain in function form so it can be manipulated symbolically  or as part of a larger expression.  

If x is an array or matrix, the result is an element-wise mapping over x.

$\mathrm{with}\left(\mathrm{MTM}\right)\:$

$\mathrm{diff}\left(\mathrm{heaviside}\left(x\right)\,x\right)$

$\mathrm{Dirac}\left(x\right)$