Any matrix of rank two can be displayed as a biplot which consists of a vector for each row and a vector for each column, chosen so that any element of the matrix is exactly the inner product of the vectors corresponding to its row and to its column. If a matrix is of higher rank, one may display it approximately by a biplot of a matrix of rank two which approximates the original matrix. The biplot provides a useful tool of data analysis and allows the visual appraisal of the structure of large data matrices. It is especially revealing in principal component analysis, where the biplot can show inter-unit distances and indicate clustering of units as well as display variances and correlations of the variables.

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SUMMARYA larkov chain probability model is found to fit Tel Aviv data of daily rainfall occurrence. This accounts for the orm of the distributions of dry and of wet spells and of weather ' cycles ' which have been presented in earl r papers. Further aspects of rainfall occurrence patterns may be derived as well, and are found to fit the data. In particular, the distribution of the number of rainy days per week, month or other period is obtained. Numbers of rainy days in different months are apparently independent.