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737. Comment on [rand.dist.samp.pconst]

Section: 28.5.9.6.2 [rand.dist.samp.pconst] Status: NAD Submitter: Stephan Tolksdorf Opened: 2007-09-21 Last modified: 2016-01-28

Priority: Not Prioritized

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Discussion:

1. The discussion in point T11 above regarding probabilities() similarly applies to the method densities() of piecewise_constant_distribution.

2. The design of the constructor

   template <class InputIteratorB, class InputIteratorW> 
   piecewise_constant_distribution( InputIteratorB firstB, InputIteratorB lastB, 
                                    InputIteratorW firstW);
   

   is unnecessarily unsafe, as there is no separate end-iterator given for the weights. I can't see any performance or convenience reasons that would justify the risks inherent in such a function interface, in particular the risk that input error might go unnoticed.

Possible resolution: I propose to add an InputIteratorW lastW argument to the interface.

[ Stephan Tolksdorf adds pre-Bellevue: ]

In reply to the discussion in N2424 I'd like to make the same comments as for 736.

[ Bellevue: ]

In N2424. There is already precedent elsewhere in the library. Follows existing convention. NAD.

Proposed resolution:

See N2424 for the proposed resolution.

[ Stephan Tolksdorf adds pre-Bellevue: ]

In 28.5.9.6.2 [rand.dist.samp.pconst]:

Proposed wording a)

Change in para. 2

Constructs a piecewise_constant_distribution object with n = 1, p₀ = w₀ = 1, b₀ = 0, and b₁ = 1

and change in para. 5

A vector<result_type> whose size member returns n and whose operator[] member returns p_k the weight w_k as a double value when invoked with argument k for k = 0, ..., n-1

Proposed wording b)

Change both occurrences of

"piecewise_constant_distribution(InputIteratorB firstB, InputIteratorB lastB,
                                 InputIteratorW firstW, InputIteratorW lastW)

and change in para. 3

the length of the sequence w starting from firstW shall be at least n, *firstW shall return a value w₀ that is convertible to double, and any w_k for k >= n shall be ignored by the distribution [firstW, lastW) shall form a sequence w of length n whose leading element w₀ shall be convertible to double