Mention (continuous => piecewise-linear) function

Add a reference describing the significant points for extrapolations
on approximating continuous functions with piecewise linear functions.

Author: rakhimov

mef/stochastic_layer.rst

@@ -720,6 +720,7 @@ Piecewise-Linear Distributions
     where the :math:`b_i`'s are bounds of successive, contiguous intervals
     such that :math:`b_i < b_{i+1}` for :math:`i = 0, \dots, n-1`,
     and the :math:`w_i`'s are non-negative weights of corresponding interval bounds :math:`b_i`.
+    A piecewise-linear distribution can approximate a continuous distribution function [#HC94]_.
 
     The distribution is defined by the following probability density function:
 
@@ -748,6 +749,11 @@ Piecewise-Linear Distributions
             \sum_{i=1}^{n}(b_i - b_{i-1})[w_i(2b_i + b_{i-1}) + w_{i-1}(b_i + 2b_{i-1})]
 
 
+.. [#HC94] B. Hamann and J. L. Chen,
+           "Data point selection for piecewise linear curve approximation,"
+           Computer Aided Geometric Design, vol. 11, no. 3, pp. 289-301, 1994.
+
+
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