Causal commutative arrows

The Glasgow Haskell Compiler (GHC) is a well supported optimizing compiler for the Haskell programming language, along with its own extensions to the language and libraries. Haskell's lazy semantics imposes a runtime model which is in general difficult to implement efficiently. GHC achieves good performance across a wide variety of programs via aggressive optimization taking advantage of the lack of side effects, and by targeting a carefully tuned virtual machine. The Intel Labs Haskell Research Compiler uses GHC as a frontend, but provides a new whole-program optimizing backend by compiling the GHC intermediate representation to a relatively generic functional language compilation platform. We found that GHC's external Core language was relatively easy to use, but reusing GHC's libraries and achieving full compatibility were harder. For certain classes of programs, our platform provides substantial performance benefits over GHC alone, performing 2x faster than GHC with the LLVM backend on selected modern performance-oriented benchmarks; for other classes of programs, the benefits of GHC's tuned virtual machine continue to outweigh the benefits of more aggressive whole program optimization. Overall we achieve parity with GHC with the LLVM backend. In this paper, we describe our Haskell compiler stack, its implementation and optimization approach, and present benchmark results comparing it to GHC.

The Glasgow Haskell Compiler (GHC) has quite sophisticated support for concurrency in its runtime system, which is written in low-level C code. As GHC evolves, the runtime system becomes increasingly complex, error-prone, difficult to maintain and difficult to add new concurrency features.This paper presents an alternative approach to implement concurrency in GHC. Rather than hard-wiring all kinds of concurrency features, the runtime system is a thin substrate providing only a small set of concurrency primitives, and the remaining concurrency features are implemented in software libraries written in Haskell. This design improves the safety of concurrency support; it also provides more customizability of concurrency features, which can be developed as Haskell library packages and deployed modularly.

Numerous papers were published during the last decade on the normal forms of nonlinear control systems with applications in bifurcation and its control. The approach is motivated by Poincare’s theory of normal forms for classical dynamical systems using homogeneous transformations. In this paper, we summarize a variety of control system normal forms published in the literature so that the normal forms are derived in a same framework with consistent notations. Before we get into technical details, the rest of the introduction is a review of existing results on some related topics. It is well known that there are several normal forms for a linear control system. If the system is controllable then the system can be transformed into controllable or controller normal form. If the system has a linear output map and is observable then it can be transformed into observable or observer form. The nonlinear generalization of the linear controller normal forms were extensively studied during 1980’s, for instance, Krener [23], Hunt-Su [11], JackubczykRespondek [10], and Brocket [3], etc. If a nonlinear control system admits a controller normal form, it can be transformed into a linear system by a change of coordinates and feedback. Therefore, the design of a locally stabilizing state feedback control law is a straightforward task. In such a case, we say the system is feedback linearizable. On the other hand, most nonlinear systems do

Expressing algorithms using immutable arrays greatly simplifies the challenges of automatic SIMD vectorization, since several important classes of dependency violations cannot occur. The Haskell programming language provides libraries for programming with immutable arrays, and compiler support for optimizing them to eliminate the overhead of intermediate temporary arrays. We describe an implementation of automatic SIMD vectorization in a Haskell compiler which gives substantial vector speedups for a range of programs written in a natural programming style. We compare performance with that of programs compiled by the Glasgow Haskell Compiler.

A limited form of dependent types, called Generalized Algebraic Data Types (GADTs), has recently been added to the list of Haskell extensions supported by the Glasgow Haskell Compiler. Despite not being full-fledged dependent types, GADTs still offer considerably enlarged scope for enforcing important code and data invariants statically. Moreover, GADTs offer the tantalizing possibility of writing more efficient programs since capturing invariants statically through the type system sometimes obviates entire layers of dynamic tests and associated data markup. This paper is a case study on the applications of GADTs in the context of Yampa, a domain-specific language for Functional Reactive Programming in the form of a self-optimizing, arrow-based Haskell combinator library. The paper has two aims. Firstly, to explore what kind of optimizations GADTs make possible in this context. Much of that should also be relevant for other domain-specific embedded language implementations, in particular arrow-based ones. Secondly, as the actual performance impact of the GADT-based optimizations is not obvious, to quantify this impact, both on tailored micro benchmarks, to establish the effectiveness of individual optimizations, and on two fairly large, realistic applications, to gauge the overall impact. The performance gains for the micro benchmarks are substantial. This implies that the Yampa API could be simplified as a number of "pre-composed" primitives that were there mainly for performance reasons are no longer needed. As to the applications, a worthwhile performance gain was obtained in one case whereas the performance was more or less unchanged in the other.

We describe a monadic interface to low-level hardware features that is a suitable basis for building operating systems in Haskell. The interface includes primitives for controlling memory management hardware, user-mode process execution, and low-level device I/O. The interface enforces memory safety in nearly all circumstances. Its behavior is specified in part by formal assertions written in a programming logic called P-Logic. The interface has been implemented on bare IA32 hardware using the Glasgow Haskell Compiler (GHC) runtime system. We show how a variety of simple O/S kernels can be constructed on top of the interface, including a simple separation kernel and a demonstration system in which the kernel, window system, and all device drivers are written in Haskell.

The most widely available high performance platforms today are multilevel clusters of multicores. The Glasgow Haskell Compiler (GHC) provides a number of parallel Haskell implementations targeting different parallel architectures. In particular, GHC-SMP supports shared memory, and GHC-GUM supports distributed memory machines. Both implementations use different, but related, runtime environment (RTE) mechanisms. Good performance results can be achieved on shared memory architectures and on networks individually. However, a combination of both, for networks of multicores, is lacking.We present the design and implementation of a new parallel Haskell RTE implementation, GUMSMP, which exploits hierarchical platforms more effectively. It is designed to efficiently combine distributed memory parallelism, using a virtual shared heap over a cluster, with low-overhead shared memory parallelism on the multicores. Key design objectives for realising this system are: asymmetric load balance, effective latency hiding, and mostly passive load distribution.We show that the automatic hierarchical load distribution policies must be carefully tuned to obtain good performance, showing the impact of several policies, including work pre-fetching and favouring inter-node work distribution. We present the initial performance results for this implementation, demonstrating the good scalability of a set of 8 benchmarks on up to 100 cores, and show performance gains of up to 20% compared to GHC-GUM.

We have developed a new, portable I/O event manager for the Glasgow Haskell Compiler (GHC) that scales to the needs of modern server applications. Our new code is transparently available to existing Haskell applications. Performance at lower concurrency levels is comparable with the existing implementation. We support millions of concurrent network connections, with millions of active timeouts, from a single multithreaded program, levels far beyond those achievable with the current I/O manager. In addition, we provide a public API to developers who need to create event-driven network applications.

A man-machine control system is described which is designed specifically for use with computerized data processing in operational numerical weather analysis and prognosis. The equipment configuration and organization of programs and data libraries in this system at the Melbourne World Meteorological Center is briefly described, together with an account of the computer activities and data flow needed in the weather analysis and prognosis data processing system. A manually interactive automatic control system, consisting of a data-driven real-time monitor program on the one hand and a data-driven visual display program on the other, was programmed to operate in parallel with all programmed meteorological activities. The interactive portion of the control system serves as the primary interface between the meteorologist and the computer equipment and operational program complex, allowing him facilities to select directly and modify the characteristics of both the data and programs being used. The flexibility of the system is well suited to the nature of weather data processing in the Southern Hemisphere, which, as a result of vast sparse data regions, must admit of a high degree of manual interaction for acceptable results. The implementation of the interactive control system results in a large saving of time in manual handling of programs and data, and reduces human error, at the same time adhering to, and warning of departures from, a preset time table of operations.

A new normal form, namely, object-normal form (ONF), is introduced. It is shown that the existing definitions of the fifth normal form (5NF) are unsatisfactory. The correct definition is given for the first time. The importance of the 5NF is demonstrated. For improving data representation in a database with a 5NF schema, the notion of negating relation is introduced. It serves as a basis for the new normal form, namely, the sixth normal form. Combining requirements of the ONF and other normal forms, new normal forms are defined: the fourth object-normal form, the fifth object-normal form, and the sixth object-normal form. It is shown that the standard order of steps of the normalization procedure should be changed: first, the specific requirements of the fourth normal form should be satisfied, and only then the requirements of the second normal form, and so forth.

We explore the convergence/divergence of the normal form for a singularity of a vector field on ℂ n with nilpotent linear part. We show that a Gevrey-α vector field X with a nilpotent linear part can be reduced to a normal form of Gevrey-1+α type with the use of a Gevrey-1+α transformation. We also give a proof of the existence of an optimal order to stop the normal form procedure. If one stops the normal form procedure at this order, the remainder becomes exponentially small.

This paper focuses on realization of high per- formance motion control based on acceleration control. A high sampling frequency is known to be effective for improving the performance. Characteristics of acceleration control are investigated and the relationship between the performance and the sampling frequency of the system is discussed. Based on these considerations, a new multirate sampling method for the acceleration control system is proposed. Disturbance observer is redesigned for application in the multirate system. Stability analysis is performed to verify the validity of the proposal. Feasibility of the proposal and influence on the performance are also verified by experimental results. frequency of acceleration control. The needs of a higher sampling frequency for output than for input are de- scribed. From this point of view, this paper proposes a new multirate sampling method with a shorter output sampling period for improvement of acceleration control performance. Disturbance observer is redesigned to fit to the multirate system with a new definition of dis- turbance torque. Stability analysis is performed to make a comparison with single-rate control and to verify the validity of the proposal. Experimental results support the feasibility of the proposed method and improvement of the performance. This study considers the system in the 1st dimension for simplicity.

In this paper, the coordinated control of active steering and active roll control systems is investigated aiming to enhance vehicle lateral dynamics performance. A combined control structure is employed to design active steering controller, in which feedback controller is designed using robust mixed sensitivity control approach to minimise the tracking error of yaw rate and body sideslip angle. To further improve vehicle cornering capacity, an active roll controller based on the yaw rate feedback is designed by re-distributing roll moments between the front and rear axles to collaborate together with active steering. The proposed control system is evaluated via computer simulations under different manoeuvres. The simulation results show the overall performance improvement using the proposed coordinated control system in terms of the better handling performances.

This work addresses two issues in lightweight structural composites suitable for aerospace systems. The first is to add additional functionality to multifunctional composites and the second is to provide damping in structures that cover a wide range of frequencies and temperatures. Passive damping in all materials suffer from failing at certain temperature and in certain frequency ranges. The extreme environments often seen by aerospace structures provide high temperature, which is exactly where damping levels in structures reduce causing unacceptable vibrations. In addition, as loading frequencies decrease damping levels fall off, and many loads experienced by aerospace structures are low frequency. This work looks at the implementation of a control system to a longitudinal metastructure bar. A metastructure is a structure which has distributed vibration absorbers which provide passive damping to the system. The active control system will be implemented by adding piezoelectric materials to one of the absorbers to make the absorber active. The structure with the active vibration absorber will be compared to a structure of equal weight with no active components. Since the two comparison structures are of equal weight, the performance improvements are strictly due to the control system and not at the cost of additional weight.

The stabilisation problem of a more general switched non‐linear system originated from the aero‐engine control systems is investigated under an average dwell‐time approach. First, a procedure of choosing coordinates transformations for individual subsystems is presented. Through these coordinates transformations, the original subsystems are transformed into their non‐linear normal forms, respectively, based on which the state feedback controllers and the Lyapunov functions for subsystems are obtained through a constructive design method. However, each subsystem and its own Lyapunov function are expressed in individual coordinates and a common coordinates transformation cannot be obtained, which makes the design of a switching law extremely difficult. The authors overcome this difficulty to construct a switching law with average dwell time which can guarantee asymptotic stability of the closed‐loop switched system. Finally, the proposed switched controller is applied to a switched model of turbofan engine, and simulation results show the feasibility and validity of the developed controller.