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C++ API

: expint (x)

Compute the exponential integral:

           infinity
          /
E_1 (x) = |exp (-t)/t dt
          /
         x

Note: For compatibility, this functions uses the MATLAB definition of the exponential integral. Most other sources refer to this particular value as E_1 (x), and the exponential integral as

            infinity
           /
Ei (x) = - |exp (-t)/t dt
           /
         -x

The two definitions are related, for positive real values of x, by E_1 (-x) = -Ei (x) - i*pi.

Package: octave