A Sigmoid Approximation of the Standard Normal Integral

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erf(z)x1l;.tryY] ,,,. Cody [tf] proposed an approximation of the erf(z) using rational frac- tions in three positive Z-range intervals and then converted the erf(z) val-.
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A Sigmoid Approximation of the Standard Normal Integral Gary R. Waissi and Donald F. Rossin School of Management Uni.aersity ol Michig an' D earbom Dearbonr, Michigan 48 1 28 Tiansmitted by Melvin Scott

ABSTRACT This paper presents a simple sigmoid function for approximation of cumulative sta,ndard normal probabilities. The approximation has an etror of t0.000043 for

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