Add documentation usecases (#249)

Author: tomasonjo

doc/connected-components.adoc

@@ -13,11 +13,14 @@ For example, consider the problem of identifying partitions in a set of items.
 We can represent each item by a node and add an edge between each pair of items that are deemed similar. 
 The connected components of this graph correspond to different classes of items.
 
+== When to use it / use-cases
+
 Testing whether a graph is connected is an essential preprocessing step for every graph algorithm. 
 Such tests can be performed so quickly and easily that you should always verify that your input graph is connected, even when you know it has to be. 
 Subtle, difficult-to-detect bugs often result when your algorithm is run only on one component of a disconnected graph.
 
-== When to use it / use-cases
+Connected components have other practical use cases, for example, if we are analysing a social network and we want to find all the disconnected groups of people that exist in our graph. 
+
 
 == Constraints / when not to use it
 

doc/label-propagation.adoc

@@ -15,7 +15,10 @@ The simplicity and time efficiency of the LPA make it a popular graph partitioni
 
 == When to use it / use-cases
 
-
+Label propagation is an algorithm for finding communities ( partitions ).
+It is one of the state-of-the-art methods, which estimates labels by propagating label information through a graph.
+Label propagation assumes that nodes connected in a graph should have similar labels.
+Consequently, the label estimation heavily depends on relationships in a graph which represent similarity of each node pair.
 
 == Constraints / when not to use it
 

doc/pagerank.adoc

@@ -27,6 +27,22 @@ PageRank is now widely recognized as a way of detecting central nodes in a netwo
 
 == When to use it / use-cases
 
+The mathematics of PageRank are entirely general and apply to any graph or network in any domain. 
+Thus, PageRank is now regularly used in bibliometrics, social and information network analysis, and for link prediction and recommendation. 
+It's even used for systems analysis of road networks, as well as biology, chemistry, neuroscience, and physics.
+
+In neuroscience, the PageRank of a neuron in a neural network has been found to correlate with its relative firing rate.
+
+Personalized PageRank is used by Twitter to present users with other accounts they may wish to follow.
+
+
+PageRank has been used to rank spaces or streets to predict how many people (pedestrians or vehicles) come to the individual spaces or streets. In lexical semantics it has been used to perform Word Sense Disambiguation,Semantic similarity, and also to automatically rank WordNet synsets according to how strongly they possess a given semantic property, such as positivity or negativity.
+
+In any ecosystem, a modified version of PageRank may be used to determine species that are essential to the continuing health of the environment.
+
+For the analysis of protein networks in biology PageRank is also a useful tool.
+
+Pagerank has recently been used to quantify the scientific impact of researchers. The underlying citation and collaboration networks are used in conjunction with pagerank algorithm in order to come up with a ranking system for individual publications which propagates to individual authors. The new index known as pagerank-index (Pi) is demonstrated to be fairer compared to h-index in the context of many drawbacks exhibited by h-index.
 
 == Constraints / when not to use it
 

doc/single-shortest-path.adoc

@@ -14,6 +14,16 @@ At that time making long-distance calls in the U.S.A. was automatized, and alter
 
 == When to use it / use-cases
 
+Shortest path algorithms are applied to automatically find directions between physical locations, such as driving directions on web mapping websites like MapQuest or Google Maps. 
+
+If one represents a nondeterministic abstract machine as a graph where nodes describe states and relationships describe possible transitions, shortest path algorithms can be used to find an optimal sequence of choices to reach a certain goal state, or to establish lower bounds on the time needed to reach a given state. 
+For example, if nodes represent the states of a puzzle like a Rubik's Cube and each directed relationship corresponds to a single move or turn, shortest path algorithms can be used to find a solution that uses the minimum possible number of moves.
+
+In a networking or telecommunications mindset, this shortest path problem is sometimes called the min-delay path problem and usually tied with a widest path problem. 
+For example, the algorithm may seek the shortest (min-delay) widest path, or widest shortest (min-delay) path.
+
+Other applications, often studied in operations research, include plant and facility layout, robotics, transportation, and VLSI design.
+
 == Constraints / when not to use it
 
 == Algorithm explanation on simple sample graph

doc/strongly-connected-components.adoc

@@ -12,6 +12,11 @@ The first linear-time algorithm for strongly connected components is due to Tarj
 
 == When to use it / use-cases
 
+_SCC_ algorithms can be used as a first step in many graph algorithms that work only on strongly connected graph.
+In social networks, a group of people are generally strongly connected (For example, students of a class or any other common place). 
+Many people in these groups generally like some common pages or play common games. 
+The SCC algorithms can be used to find such groups and suggest the commonly liked pages or games to the people in the group who have not yet liked commonly liked a page or played a game.
+
 == Constraints / when not to use it
 
 == Algorithm explanation on simple sample graph