Wrapping layered graphs

We present additions to the widely-used layout method for directed acyclic graphs of Sugiyama et al. [16] that allow to better utilize a prescribed drawing area. The method itself partitions the graph's nodes into layers. When drawing from top to bottom, the number of layers directly impacts the height of a resulting drawing and is bound from below by the graph's longest path. As a consequence, the drawings of certain graphs are significantly taller than wide, making it hard to properly display them on a medium such as a computer screen without scaling the graph's elements down to illegibility. We address this with the Wrapping Layered Graphs Problem (WLGP), which seeks for cut indices that split a given layering into chunks that are drawn side-by-side with a preferably small number of edges wrapping backwards. Our experience and a quantitative evaluation indicate that the proposed wrapping allows an improved presentation of narrow graphs, which occur frequently in practice and of which the internal compiler representation SCG is one example

Sugiyama Layouts for Prescribed Drawing Areas

The area of graph drawing is concerned with positioning the elements of a graph on a canvas such that the resulting drawing is well-readable by humans and aids their execution of certain tasks. While known methods are usually well-studied from a theoretical perspective, both their applicability to graphs from practice and their integration into tools from practice are not always satisfactory. This is due to various reasons, for instance, due to known methods usually solving well-defined, self-contained problems that do not cover all of the bits and pieces that must be considered in practice. There, the diagrams the graphs originate from often comprise more than just simple nodes and simple edges, they tend to be messy and complex, and existing methods regularly compute drawings with poor compactness. This thesis is concerned with improving the well-known layer-based layout approach, originally proposed by Sugiyama et al., and devotes special attention to the requirements of dataflow diagrams. It presents new methods for the approach's layer assignment and coordinate assignment steps, and it identifies and illustrates research tasks that are essential to further better the situation in practice

Using One-Dimensional Compaction for Smaller Graph Drawings

We review the technique of one-dimensional compaction and use it as part of two new methods tackling problems in the context of automatic diagram layout: First, a postprocessing of the layer-based layout algorithm, also known as Sugiyama layout, and second a placement algorithm for connected components with external extensions. We apply our methods to dataflow diagrams from practical applications and find that the first method significantly reduces the width of left-to-right drawn diagrams. The second method allows to properly arrange disconnected graphs that have hierarchycrossing edges. Keywords: one-dimensional compaction, diagram layout, layer-based layout, Sugiyama layout, disconnected graphs, dataflow diagram

Drawing Layered Hypergraphs

Orthogonally drawn hypergraphs have important applications, e.g. in actor-oriented data flow diagrams for modeling complex software systems. Graph drawing algorithms based on the approach by Sugiyama et al. place nodes into consecutive layers and try to minimize the number of edge crossings by finding suitable orderings of the nodes in each layer. With orthogonal hyperedges, however, the exact number of crossings is not determined until the edges are actually routed in a later phase of the algorithm, which makes it hard to evaluate the quality of a given node ordering beforehand. In this report, we present and evaluate two crossing counting algorithms that predict the number of crossings between orthogonally routed hyperedges much more accurately than previous methods. We also describe methods for routing hyperedges that span multiple layers and for handling junction points

Minimum-width graph layering revisited

The minimum-width layering problem tackles one step of a layout pipeline to create top-down drawings of directed acyclic graphs. Thereby, it aims at keeping the overall width of the drawing small. We study layering heuristics for this problem as presented by Nikolov et al. as well as traditional layering methods with respect to the questions how close they are to the true minimal width and how well they perform in practice, especially, if a particular drawing area is prescribed. We find that when applied carefully and at the right moment the layering heuristics can, compared to traditional layering methods, produce better layerings for prescribed drawing areas and for graphs with varying node dimensions. Still, we also find that there is room for improvement

Challenges and approaches in data management of LTE trials in tropical field sites: Experiences from two trials in India and Bolivia

Quality data is the key commodity of research projects. But with the size of a research project, number of parties involved and range of data collected, the complexity of data management increases significantly. In long-term experiments (LTE), continuity and comparability of collected data throughout the study duration is important but being challenged by personnel changes and development in infrastructure and technology, as well as changes to the trial itself. Managing a longterm trial remotely at field sites in the tropics adds another layer of challenges, including timely transfer of new data, time consuming pre-processing and validation of data between field and scientific staff, data literacy of local field staff and language barriers due to varying levels of English and local languages within the project team. We share our challenges in data management and the strategies and tools used in the context of two LTE trials with field sites in India and Bolivia, managed by local partner organizations and coordinated by the Research Institute of Organic Agriculture in Switzerland, highlighting the technical infrastructure in use, definition of responsibilities and workflows. Our main considerations are a) finding a balance between data security, easy and timely sharing of data in both directions and minimising number of different data repositories and file versions, b) the use of simple, well-known tools that are flexible enough to consider (evolving) needs of different involved parties including field staff, and c) the importance of quick data availability for analysis to serve as a basis for decision making in trial management

Productivity and income in 5 different cocoa production systems

Cocoa agroforestry systems, combining cocoa with timber and fruit trees, are mainly promoted for their environmental benefits. Knowledge gaps exist about the economic performance of such systems. Here we present the productivity and income of 5 cocoa production systems from planting to entering the mature stage 11 years)

Different agroforestry designs for diversified organic cocoa production – cocoa and by-crop yield development in 11 years of a long-term trial

Agroforestry systems for cocoa production are commonly promoted for biodiversity conservation, climate change mitigation and adaptation as well as for food security and risk mitigation. Generally, these systems include timber, legume or fruit trees. Sucessional or dynamic agroforestry systems represent a special type of design and management approach, using high densities and diversity of trees and crops occupying different strata and with varying life cycles. Here we present results on absolute and potential yields of 3 organic cocoa production systems entering the mature stage from a long-term trial in Bolivia: A complex successional dynamic agroforestry system (SAFS), a simpler but diversified agroforestry system (AF ORG) and a cocoa monoculture (MONO ORG). Cocoa yields were highest in MONO ORG, followed by the AF ORG, and lowest in SAFS. Total system yields in both types of agroforestry systems (dry matter) were 3.5 to 4 times higher than in monocultures over the 11 years. This was mainly due to banana production in AF ORG and from a multitude of by-crops in SAFS. In mature SAFS peach palm was the by-crop with the highest dry matter production. The results demonstrate how different crops can be associated with cocoa while still reaching elevated cocoa yields. The potential of agroforestry systems to sustainably intensify production on one surface is high and could still be optimised with the use of improved and locally selected varieties of cocoa and fruit trees. Different designs of agroforestry systems can contribute to diversification of diets and incomes of producing families and regions

Economic Performance of Five Different Cacao Production Systems

Agroforestry systems for cocoa production are commonly promoted for biodiversity conservation, climate change mitigation and adaptation as well as for food security and risk mitigation. Generally, these systems include timber, legume or fruit trees, and sometimes additional crops. Knowledge gaps exist about the economic performance of cocoa based agroforestry systems, including the by-crops. Here we present the economic performance of 5 cocoa production systems from planting to entering the mature stage (11 years). In a long-term trial in Bolivia, a gradient of complexity from monocultures, agroforestry systems to successional agroforestry systems (SAFS) is studied. Additionally, for monocultures and agroforestry, conventional and organic management are compared, while SAFS are managed organically. Income was calculated taking into account yields of cocoa, fruit trees and by-crops with farm gate prices. Only for cocoa organic premium prices were reached and taken into account. Labour time was registered for management, input preparation and post-harvest. Cocoa yields were lower in the agroforestry systems compared with monocultures, and lowest in SAFS. For monocultures, they were higher under conventional management, while in agroforestry systems management had no influence. Total system yields in agroforestry systems (dry matter) were 3–4 times higher than in monocultures. This was mainly due to banana production in agroforestry systems and from a diversity of by-crops in SAFS. Income over all years was comparable among all systems. In agroforestry systems, cocoa was responsible for more than 50 % of the income, while in SAFS the share of cocoa was smaller, as some crops like pineapples or peach palm had good markets in the region. The income generated per workday invested during the whole period did not differ between the systems. Income analysis shows the importance of cocoa as a cash crop, but also the potential of by-crops depending on the development of their markets. On the other hand, agroforestry systems contribute to food security and mitigate risks of price or yield fluctuations in the cash crop. In conclusion, the data show that with different strategies and plantation design, the same level of income and income per work day invested can be reached. More information on the trial layout can be found here: https://systems-comparison.fibl.or

Size- and Port-Aware Horizontal Node Coordinate Assignment

The approach by Sugiyama et al. is widely used to automatically draw directed graphs. One of its steps is to assign horizontal coordinates to nodes. Brandes and Koepf presented a method that proved to work well in practice. We extend this method to make it possible to draw diagrams with nodes that have considerably different sizes and with edges that have fixed attachment points on a node’s perimeter (ports). Our extensions integrate seamlessly with the original method and preserve the linear execution time