This member function initializes the invoking function as a step function whose steps are defined by the two arguments arrays x and v. More precisely, if n is the size of array x, size of array v must be n+1 and, if the invoking function is defined on the interval [xMin,xMax), its values will be:

• v[0] on interval [xMin,x[0]),
• v[i] on interval [x[i-1],x[i]) for all i in [0,n-1], and
• v[n] on interval [x[n-1],xMax).