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Subsections

EXPEI Exponential Weighted Integral Function

Usage

Computes the exponential weighted integral function for real arguments. The expei function takes only a single argument

  y = expei(x)

where x is either a float or double array. The output vector y is the same size (and type) as x.

Function Internals

The expei function is defined by the integral:

$\displaystyle \mathrm{expei}(x) = - e^{-x} \int_{-x}^{\infty} \frac{e^{-t} dt}{t}.
$

Example

Here is a plot of the expei function over the range [-5,5].

--> x = linspace(-5,5);
--> y = expei(x);
--> plot(x,y); xlabel('x'); ylabel('expei(x)');

which results in the following plot.

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Samit K. Basu 2005-03-16