Comments, with reply, on `On the projection method for protocolverification' by T.-Y. Cheung

A counterexample to a theorem given in a paper by T.-Y. Cheung (see ibid., vol.12, no.11, p.1088-9, 1986) is given. In a reply, the author of the original paper argues that the counterexample is not correct     

Comments on `On blocking zeros in linear multivariable systems'[with reply]

Reference is made to a recently published correspondence by P.G. Ferreira in which concern was expressed about the name `blocking zeros' given in a paper by R.V. Patel (see ibid., vol.AC-31, p.239-41, Mar. 1986) to a newly defined class of zeros for multivariable linear systems. The commenter refers to a few remarks about some `well-known' results by Ferreira, and objects to the lack of precision in the wording of two of these remarks. Counterexamples to these `well-known' results are presented. In replying, the original author claims that Example 1 is not a counterexample to his statement, and objects to some lack of precision in Martin's words     

Comments on `On the stability of discrete-time sliding mode controlsystems' [with reply]

In the above paper by S.Z. Sarpturk and Y. Istefanopulos (see IEEE Trans. Automat. Contr., vol.AC-32, p.930-2 (1987)), stability conditions for discrete-time sliding mode control systems are presented, which require the stabilizing control to be upper and lower bounded. The present author shows that these bounds depend on the distance of the system state from the sliding manifold and that they converge as the state approaches the manifold. Sarpturk and Istefanopulos agree that the bounds of the discrete-time control guaranteeing the stability of the sliding mode system depend also on the distance of the state from the sliding manifold. Therefore, in order to guarantee the stability of the sliding mode system, the controls must be chosen so as to satisfy the convergence and sliding bounds derived in the paper     

Comments on `On the adiabatic approximation for design of controllaws for linear, time-varying systems' [with reply]

An example is used to demonstrate that in the abovementioned paper by B. Friedland et al. (ibid., vol.AC-32, pp.62-3, Jan. 1987) the theorem on asymptotic stability has to be used in a more precise form than cited to yield a stable feedback controller. The authors thank the commenter for pointing this out     

Comments on `On adaptive inverse dynamics control of rigid robots'[with reply]

The commenters point out an error in the adaptive control approach for robotic manipulators given in the above-named work by M.W. Spong and R. Ortega (see ibid., vol.35, p.92-5, Jan. 1990). It is noted that the authors assert that their adaptive control scheme eliminates the restriction given in J.J. Craig (1986) on the estimated inertia matrix; however, the commenters point out that a form of the inverse of the estimated inertia matrix must be bounded for the acceleration to be bounded. In a reply, the authors acknowledge the error in their paper     

Comments. with reply, on `Tip of the flowchart iceberg' by D.A.Scanlan

The commenters maintain that the study in the above article (see ibid., vol.6, no.5, p.28-36 (1990)) reveals only the tip of a massive iceberg because the author restricts his attention to flowcharts. They report that their experience in developing and using graphical representations based on valuation contexts suggests that when graphical methods are fully appreciated and used, they will radically change the way we think about systems and the way we practice software development. They disagree with the claim that some of Scanlan's examples are unrealistically complex. The author thanks the commenters for their favorable and insightful comments about the importance of graphics to depict complex systems. He maintains his position that the most complex algorithm in the experiment was unrealistically complex     

Comments, with reply, on `Techniques for selective revalidation' byJ. Hartmann and D.J. Robson

The commenter points out the disadvantages of the selective testing approach advocated by the authors of the above-titled paper (see ibid., vol.7, no.1, p.31-36, 1990). He proposes the use of bottom-up testing. J. Hartmann agrees with the commenter on the advantages of bottom-up testing for development and maintenance and points out this approach is used in the article as part of the selective-revalidation strategy     

Comments, with reply, on `Computational algorithms for poleassignment' by N.K. Nichols

Some points of the paper by N.K. Nichols (see ibid., vol.AC-31, p.643-5, 1986), concerning the robust pole assignment of linear multiinput systems, are clarified. It is stressed that the minimization of the condition number of the closed-loop eigenvector matrix does not necessarily lead to robustness of the pole assignment. It is shown why the computational method, which Nichols claims is robust, is in fact numerically unstable with respect to the determination of the gain matrix. In replying, Nichols presents arguments to support the choice of the conditioning of the closed-loop poles as a measure of robustness and to show that the methods of J Kautsky, N. K. Nichols and P. VanDooren (1985) are stable in the sense that they produce accurate solutions to well-conditioned problems     

Comments, with reply, on 'Structured flowcharts outperform pseudocode: an experimental comparison' by D.A. Scanlan

The commenter maintains that what is being compared in the abovementioned article (see ibid., vol.6, no.5, p.28-36 (1989)) is the relative stability of flowcharts and pseudocode for the expression of a restricted aspect of actual programs, better isolated in the lab than in practice. He notes that the author avoids any loops in his three test algorithms. He points out that flowcharts require special output capabilities and an elaborate editor if they are to compare as a tool with pseudocode. The author responds that the commenter's point about the lack of loops in the algorithms is well taken but that he chose algorithms very similar to those used in a study with which he wished to compare his results. He addresses other points made by the commenter, defending his own approach and conclusions.<>     

Comments, with reply, on `The standardization line' by A. Winder

The commenter maintains that the author of the above-titled article (see ibid., vol.7, no.3, p.84-85, 1990) failed to consider psychological, sociological and design aspects of the subject of naming conventions, and he discusses some research that has been done on these issues. The author responds that the commenter's points are valid if naming standards is viewed as an isolated exercise. She points out, however, that the naming scheme she described assumes a context, which is to normalize an organization's data and business practices     

Comments on `On the robust control of robot manipulators by M.W.Spong

In the above-title paper (ibid., vol.37, no.11, pp.1782-1786, Nov. 1992) a simple robust control is given for guaranteeing uniform ultimate boundedness of tracking errors for n-link robot manipulators. It is pointed out here that an equally simple control law, which is also continuous in nature, can guarantee global exponential stability of tracking errors under the same set of conditions     

Comments, with reply, on `Extensions to SQL for historicaldatabases' by N.L. Sarda

The commenters point out that the author of the above-titled paper (see ibid., vol.2, p.220-30, 1990) failed to acknowledge their contemporary publications of almost identical results and the subsequent, comprehensive refinement of this work. The author replies that he did not have access to their publications. He indicates some differences between their work and his     

Comments on `On the stability of uncertain polynomials withdependent coefficients by L.R. Pujara

It is pointed out that the two main results in the above-titled paper (ibid, vol.35, pp.756-759, Jun 90) are closely related to a previously published result     

Comments, with reply, on `Is copyright law steering the rightcourse' by P. Samuelson

The commenter offers an additional point that the above mentioned article (see ibid., vol.5, no.5, p.78-86, Sept.1988) did not address. He suggests that one of the purposes of copyright and patent law is to promote progress of the sciences and the arts, and he presents arguments to support his point     

Comments, with reply, on `The universal-relation data model forlogical independence' by M. Vardi

The commenter contends that the universal-relation data model proposed in the above mentioned paper (ibid., vol.5, no.2, p.80-5, Mar. 1988) fails completely as an alternative to the relational data model, and presents supporting arguments. The author replies that the commenter has read into the article claims that are not there and rebuts the commenters arguments point by point     

Comments, with reply, on `Fast convolution withLaplacian-of-Gaussian masks' by J.S. Chen et al

In a recent paper by J.S. Chen et al. (ibid., vol.PAMI-9, p.584-90, July 1987) the authors presented a means of decomposing the Laplacian-of-Gaussian (LoG) kernel into the product of a Gaussian and a (smaller) LoG mask. They then proceeded to develop a fast algorithm for convolution which exploits the spatial frequency properties of these operators to allow the image to be decimated (subsampled). Although this approach is both novel and interesting, it is contended that the exposition suffers from some inconsistencies and minor errors. The commenters clarify matters for those who wish to implement this technique. The original authors acknowledge two of the three points raised, and provide further clarification of the other one namely, the claim that the masks (Gaussian and LoG) are too small     

Comments, with reply on `Third-generation versus fourth-generationsoftware development'' by S. Misra and P. Jalics

The computer argues that the conclusion to be drawn from the above mentioned article (see ibid., vol.5, no.4, p.8-14, July 1988), that there is no need for fourth-generation languages and no advantage in using them is questionable. He considers the experimental setup in the July article questionable and raises a number of substantive questions about it. The authors reply that there is no suggestion in their article that fourth-generation languages are not needed, but that they are not prepared to accept any tool as a fourth-generation language just because it is labeled as such. They respond to each of the commenter's points and propose a necessary condition of a fourth-generation language     

Comments, with reply, on `Adding data abstraction to FortranSoftware' by K.W. Miller, et al

The commenter observes that the history of using preprocessors to add data types to Fortran is richer than indicated in the above article (see ibid., vol.5, no.6, p.50-8, Nov. 1988). He mentions a number of efforts, including one of his own, called Augment, which is similar to the FAD system described in the article. One of the authors, K.W. Miller, replies that he was unaware of Crary's work and comments on the Augment system     

Comments, with reply, on `Estimating the robust dead time forclosed-loop stability' by A.K. El-Sakkary

The commenters illustrate how easy it is to find the upper bound on the robust dead time for closed-loop stability as compared to a method for obtaining only its estimate, proposed in the above-mentioned paper (ibid., vol.33, no.6, p.599-601, June 1988). The author restates his main result and shows that it serves a purpose that was overlooked by the commenters