【正文】 high and low series impedances, long EHV lines, series and shunt pensation in the model of power flow problem, diagonal dominance will be weaken [8] and the assumption may not be tenable invariably. Furthermore, along with the development of modern power systems, various new models with parameters under various orders of magnitude appear in the model of power flow. The promotion of distributed generation also encourage us to regard the distribution works and transmission systems as a whole in power flow calculation, and it will cause more serious numerical problem. All those things mentioned above will turn the problem into illcondition. So it is necessary to discuss the effect of the node numbering to the accuracy of the solution. Based on the existing node ordering algorithm mentioned above, this paper focus attention on the contradiction between memory and accuracy during node ordering, research how could node ordering algorithm affect the performance of power flow calculation, expecting to lay groundwork for the more rationality ordering algorithm. This paper is arranged as follows. The contradiction between memory and accuracy in node ordering algorithm is introduced in section II. Next a simple DC power flow is showed to illustrate that node ordering could affect the accuracy of the solution in section III. Then, taking a 6node work as an example, the effect of node ordering on the performance of power flow is analyzed detailed in section IV. Conclusion is given in section VI. II. CONTRADICTION BETWEEN MEMORY AND ACCURACY IN NODE ORDERING ALGORITHM According to numerical mathematics, plete pivoting is numerically preferable to partial pivoting for systems of liner algebraic equations by Gaussian Elimination Method (GEM). Many mathematical papers [911] focus their attention on the 外文翻譯（原 文） 4 discrimination between plete pivoting and partial pivoting in (GEM). Reference [9] shows how partial pivoting and plete pivoting affect the sensitivity of the LU factorization. Reference [10] proposes an effective and inexpensive test to recognize numerical difficulties during partial pivoting requires. Once the assessment criterion can not be met, plete pivoting will be adopted to get better numerical stability. In power flow calculations, partial pivoting is realized automatically without any rowinterchanges and columninterchanges because of the diagonally dominant features of the Jacobin matrix, which could guarantee numerical stability in floating point putation in most cases. While due to rounding errors, the partial pivoting does not provide the solution accurate enough in some illconditionings. If plete pivoting is performed, at each step of the process, the element of largest module is chosen as the pivotal element. It is equivalent to adjust the node ordering in power flow calculation. So the node relate to the element of largest module is tend to arrange in front for the purpose of improving accuracy. The node reordering algorithms guided by sparse matrix technology have wildly used in power system calculation, aiming at minimizing memory requirement. In these algorithms, the nodes with fewer adjacent nodes tend to be numbered first. The result is that diagonal entries in node admittance matrix tend to be arranged from least to largest according to their module. Analogously, every diagonal submatrices relate to a node tend to be arranged from least to largest according to their determinants. So the results obtained form such algorithms will just deviate form the principle follow which the accuracy of the solution will be enhance. That is what we say there is contradiction between node ordering guided by memory and accuracy. III. DIFFERENCE PRECISION OF THE SOLUTION USING PARTICAL PIVOTING AND COMPLETE PIVOTING It is said that plete pivoting is numerically preferable to partial pivoting for solving systems of linear algebraic equations. When the system coefficients are varying widely, the accuracy of the solution would be affect by rounding errors hardly 外文翻譯（原 文） 5 and it is necessary to take the influence of the ordering on the accuracy of the solution into consideration. DC model of Sample 4node work As an example, consider the DC model of sample 4node system shown in Figure 1. Node 1 is the swing node having known voltage angle。 node ordering。 sparsity。 nodes 24 are load nodes. Following the original node number, the DC power flow equation is: To simulate puter numerical calculation operations, four significant figures will be used to solve the problem. Executing GEM without pivoting on (1) yields the solution[ θ2,θ3,θ4]T=[,]T, whose ponents differ from that of the exact solution [θ2, θ3,θ4]T=[,]T. A more exact solution could be obtained by plete pivoting: [θ2,θ3, θ4]T=[,]T, and the order of the node after row and column interchanges is 3,2,4. So this is a more reasonable ordering scheme for the purpose of getting more high accuracy. IV. THE INFLUENCE OF NODE REODERING ON THE PERFORMANCE OF NEWTONRAPHSON POWER FLOW METHOD 外文翻譯（原 文） 6 Sample 6node work On the basis of the abovementioned analysis, the scheme for node reordering will not only affect memory requirement but also the accuracy of the solution in solving linear simultaneous equations. So performance of NewtonRaphson power flow method will be different with various node ordering. In this section three schemes of ordering for different purpose will be applie