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Monte Carlo Analysis<br />

How to Specify a Distribution Function<br />

The probability density function is expressed as:<br />

where φ and Φ represent the probability density and the cumulative distribution function<br />

respectively of the reduced centred Normal distribution (that is, the mean μ zero and standard<br />

deviation σ equal to 1).<br />

A random variable that follows a truncated Normal distribution takes values in the interval<br />

[a, b]. The parameter μ describes the most likely value. Whilst σ provides a measure of<br />

dispersion. Figure 11-6 shows an example with μ = 20, σ = 7, and [a, b] = [10, 35].<br />

In Eldo, the centered and reduced Gaussian variables are generated with the truncated normal<br />

distribution before transformation to the original scales of the input space.<br />

Figure 11-6. Plot of the Truncated Normal<br />

The bounds of the truncation interval are fixed by default to the SIGTAIL value. Note that this<br />

interval is necessarily a symmetric interval.<br />

434<br />

Eldo® User's Manual, 15.3

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