Cosine integral
From specialfunctionswiki
The cosine integral is defined by $$\mathrm{Ci}(z) = -\displaystyle\int_z^{\infty} \dfrac{\cos t}{t} dt ; |\mathrm{arg} z|<\pi.$$
The cosine integral is defined by $$\mathrm{Ci}(z) = -\displaystyle\int_z^{\infty} \dfrac{\cos t}{t} dt ; |\mathrm{arg} z|<\pi.$$
