Derivative of sine integral
From specialfunctionswiki
Theorem
The following formula holds: $$\dfrac{\mathrm{d}}{\mathrm{d}z} \mathrm{Si}(z) = \mathrm{sinc}(z),$$ where $\mathrm{Si}$ denotes the sine integral and $\mathrm{sinc}$ denotes the sinc.
