Comments on: Problem Set 3: Implementing Abstract Datatypes http://www.cs.virginia.edu/cs2220 Thu, 04 Nov 2010 18:05:57 +0000 hourly 1 http://wordpress.org/?v=3.0.1 By: David Evans http://www.cs.virginia.edu/cs2220/?page_id=255&cpage=1#comment-13 David Evans Mon, 20 Sep 2010 23:54:24 +0000 http://www.cs.virginia.edu/cs2220/?page_id=255#comment-13 The specification is less clear than it should be on this, since the prose is ambiguous, but the formal notation is more clear (but not consistent with the notation used elsewhere!): <blockquote> EFFECTS: If s is not a node in this, throws NoNodeException. Otherwise, returns a set containing the nodes adjacent to s That is, returns the set of nodes { e | <s, e> is in E } </blockquote> This suggests that it should only include nodes that can be reached following an edge from s to e. The inconsistency is the abstract notation uses (s, e) to denote edges, but the spec here incorrectly uses <s, e>. A better specification would make this more clear: <blockquote> EFFECTS: If s is not a node in this, throws NoNodeException. Otherwise, returns a set containing the nodes that can be reached following an edge from s That is, returns the set of nodes { e | (s, e) is in E } </blockquote> The specification is less clear than it should be on this, since the prose is ambiguous, but the formal notation is more clear (but not consistent with the notation used elsewhere!):

EFFECTS: If s is not a node in this, throws NoNodeException.
Otherwise, returns a set containing the nodes adjacent to s

That is, returns the set of nodes
{ e | <s, e> is in E }

This suggests that it should only include nodes that can be reached following an edge from s to e. The inconsistency is the abstract notation uses (s, e) to denote edges, but the spec here incorrectly uses <s, e>.

A better specification would make this more clear:

EFFECTS: If s is not a node in this, throws NoNodeException.
Otherwise, returns a set containing the nodes that can be reached following an edge from s

That is, returns the set of nodes { e | (s, e) is in E }

]]> By: blantonj http://www.cs.virginia.edu/cs2220/?page_id=255&cpage=1#comment-12 blantonj Mon, 20 Sep 2010 22:59:03 +0000 http://www.cs.virginia.edu/cs2220/?page_id=255#comment-12 The specification for StringGraph says that it is a directed graph, which means that each connection goes one way. For getAdjacent, then, should it include all nodes in any way connected to the input or just ones that start at the input? The specification for StringGraph says that it is a directed graph, which means that each connection goes one way. For getAdjacent, then, should it include all nodes in any way connected to the input or just ones that start at the input?

]]> By: David Evans http://www.cs.virginia.edu/cs2220/?page_id=255&cpage=1#comment-11 David Evans Mon, 20 Sep 2010 17:24:54 +0000 http://www.cs.virginia.edu/cs2220/?page_id=255#comment-11 I've fixed a couple typesetting problems with the StringGraph specification. The overview specification should list the edges as ordered pairs, instead of sets. It now reads, <blockquote> A typical StringGraph is < {v1, v2, ..., vn} , { (v_a1, v_b1), (v_a2, v_b2), ... } > where each ai and bi is in [1, n]. </blockquote> Note that the abstract representation of the edges is a set of pairs of Strings, where each string is the name of a node in the node set. Also, I fixed the specification of <tt>addEdge</tt>. There was a problem with the html, it should read <blockquote> G<sub>post</sub> = < V<sub>pre</sub>, E<sub>pre</sub> U { (<em>s</em>, <em>t</em>) } > </blockquote> to show the new edge is added to the set of edges. Sorry for the confusion! I’ve fixed a couple typesetting problems with the StringGraph specification. The overview specification should list the edges as ordered pairs, instead of sets. It now reads,

A typical StringGraph is
< {v1, v2, ..., vn} , { (v_a1, v_b1), (v_a2, v_b2), ... } >
where each ai and bi is in [1, n].

Note that the abstract representation of the edges is a set of pairs of Strings, where each string is the name of a node in the node set.

Also, I fixed the specification of addEdge. There was a problem with the html, it should read

Gpost = < Vpre, Epre U { (s, t) } >

to show the new edge is added to the set of edges.

Sorry for the confusion!

]]> By: David Evans http://www.cs.virginia.edu/cs2220/?page_id=255&cpage=1#comment-10 David Evans Sun, 19 Sep 2010 03:18:37 +0000 http://www.cs.virginia.edu/cs2220/?page_id=255#comment-10 Sorry, its an html bug. It should just be a >. Its fixed now, thanks for reporting the problem! Sorry, its an html bug. It should just be a >. Its fixed now, thanks for reporting the problem!

]]> By: bkn3yh http://www.cs.virginia.edu/cs2220/?page_id=255&cpage=1#comment-9 bkn3yh Sun, 19 Sep 2010 01:52:23 +0000 http://www.cs.virginia.edu/cs2220/?page_id=255#comment-9 In public class Poly { // Rep: private ArrayList<TermRecord&gt terms; what does &gt mean? In public class Poly {
// Rep:
private ArrayList<TermRecord&gt terms;

what does &gt mean?

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