Improve/cleanup references

Author: hannes-uppman

src/buchheim.jl

@@ -6,9 +6,8 @@ export Buchheim, buchheim
     buchheim(adj_matrix; kwargs...)
     buchheim(adj_list; kwargs...)
 
-Using the algorithm proposed in the paper,
-["Improving Walker's Algorithm to Run in Linear Time"](http://dirk.jivas.de/papers/buchheim02improving.pdf)
-by Christoph Buchheim, Michael Junger, Sebastian Leipert
+Using the algorithm proposed by Buchheim, Junger and Leipert (2002,
+[doi 10.1007/3-540-36151-0_32](https://doi.org/10.1007/3-540-36151-0_32)).
 
 Takes adjacency matrix or list representation of given tree
 and returns coordinates of the nodes.

src/sfdp.jl

@@ -4,7 +4,9 @@ export SFDP, sfdp
     SFDP(; kwargs...)(adj_matrix)
     sfdp(adj_matrix; kwargs...)
 
-Using the Spring-Electric [model suggested by Yifan Hu](http://yifanhu.net/PUB/graph_draw_small.pdf).
+Using the Spring-Electric model suggested by Hu (2005, The Mathematica Journal,
+[pdf](http://yifanhu.net/PUB/graph_draw_small.pdf)).
+
 Forces are calculated as:
 
         f_attr(i,j) = ‖xi - xj‖ ² / K ,    i<->j

src/spectral.jl

@@ -6,10 +6,9 @@ export Spectral, spectral
     Spectral(; kwargs...)(adj_matrix)
     spectral(adj_matrix; kwargs...)
 
-This algorithm uses the technique of Spectral Graph Drawing, which is an
-under-appreciated method of graph layouts; easier, simpler, and faster than the
-more common spring-based methods. For reference see [Yehuda Koren,
-2002](http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.3.2055&rep=rep1&type=pdf).
+This algorithm uses the technique of Spectral Graph Drawing.
+For reference see Koren (2003,
+[doi 10.1007/3-540-45071-8_50](https://doi.org/10.1007/3-540-45071-8_50)).
 
 Takes adjacency matrix representation of a network and returns coordinates of
 the nodes.

src/spring.jl

@@ -4,7 +4,8 @@ export Spring, spring
     Spring(; kwargs...)(adj_matrix)
     spring(adj_matrix; kwargs...)
 
-Use the spring/repulsion model of Fruchterman and Reingold (1991) with
+Use the spring/repulsion model of Fruchterman and Reingold (1991,
+[doi 10.1002/spe.4380211102](https://doi.org/10.1002/spe.4380211102)) with
 
 - Attractive force:  `f_a(d) =  d^2 / k`
 - Repulsive force:  `f_r(d) = -k^2 / d`

src/stress.jl

@@ -10,6 +10,9 @@ export Stress, stress
 Compute graph layout using stress majorization. Takes adjacency matrix
 representation of a network and returns coordinates of the nodes.
 
+The main equation to solve is (8) in Gansner, Koren and North (2005,
+[doi 10.1007/978-3-540-31843-9_25](https://doi.org/10.1007/978-3-540-31843-9_25)).
+
 ## Inputs:
 - `adj_matrix`: Matrix of pairwise distances.
 
@@ -51,23 +54,6 @@ representation of a network and returns coordinates of the nodes.
     - `(true, false, false)` : only pin certain coordinates
 
 - `seed=1`: Seed for random initial positions.
-
-## Reference:
-The main equation to solve is (8) of:
-
-    @incollection{
-        author = {Emden R Gansner and Yehuda Koren and Stephen North},
-        title = {Graph Drawing by Stress Majorization}
-        year={2005},
-        isbn={978-3-540-24528-5},
-        booktitle={Graph Drawing},
-        seriesvolume={3383},
-        series={Lecture Notes in Computer Science},
-        editor={Pach, J\'anos},
-        doi={10.1007/978-3-540-31843-9_25},
-        publisher={Springer Berlin Heidelberg},
-        pages={239--250},
-    }
 """
 @addcall struct Stress{Dim,Ptype,IT<:Union{Symbol,Int},FT<:AbstractFloat,M<:AbstractMatrix} <:
                 IterativeLayout{Dim,Ptype}