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    Am J Optom Physiol Opt. 1988 Oct;65(10):794-802.

    Algebra of sphero-cylinders and refractive errors, and their means, variance, and standard deviation.

    Source

    Department of Optometry, Rand Afrikaans University, Johannesburg, South Africa.

    Abstract

    Sphero-cylinders and refractive errors can be represented by matrices. Matrix algebra provides methods whereby sphero-cylinders can be added, subtracted, multiplied, inverted, and raised to powers and can have roots extracted. These operations are defined for sphero-cylinders and examples are given. In terms of these operations a number of means of refractive errors are defined: the arithmetic, harmonic, and quadratic means. Furthermore it is possible to define a variance and standard deviation for refractive errors. These quantities should provide a basis for a formal approach to the statistical analysis of populations of refractive errors.

    PMID:
    3207150
    [PubMed - indexed for MEDLINE]

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