Computes the probability density at x using the piecewise linear density function.
Returns 2(x - a) / ((b - a)(c - a)) for a <= x < c, 2 / (b - a) at x = c, 2(b - x) / ((b - a)(b - c)) for c < x <= b, and 0.0 outside the support.
Return
the probability density at x, always non-negative.
Parameters
x
the point at which to evaluate the density.