10.31 Power Series10.33 Continued Fractions

§10.32 Integral Representations

Contents

§10.32(i) Integrals along the Real Line

10.32.1 \mathop{I_{{0}}\/}\nolimits\!\left(z\right)=\frac{1}{\pi}\int _{0}^{\pi}e^{{\pm z\mathop{\cos\/}\nolimits\theta}}d\theta=\frac{1}{\pi}\int _{0}^{\pi}\mathop{\cosh\/}\nolimits\!\left(z\mathop{\cos\/}\nolimits\theta\right)d\theta.
10.32.2 \mathop{I_{{\nu}}\/}\nolimits\!\left(z\right)=\frac{(\frac{1}{2}z)^{\nu}}{\pi^{{\frac{1}{2}}}\mathop{\Gamma\/}\nolimits\!\left(\nu+\frac{1}{2}\right)}\int _{0}^{\pi}e^{{\pm z\mathop{\cos\/}\nolimits\theta}}(\mathop{\sin\/}\nolimits\theta)^{{2\nu}}d\theta=\frac{(\frac{1}{2}z)^{\nu}}{\pi^{{\frac{1}{2}}}\mathop{\Gamma\/}\nolimits\!\left(\nu+\frac{1}{2}\right)}\int _{{-1}}^{1}(1-t^{2})^{{\nu-\frac{1}{2}}}e^{{\pm zt}}dt, \realpart{\nu}>-\tfrac{1}{2}.
10.32.3 \mathop{I_{{n}}\/}\nolimits\!\left(z\right)=\frac{1}{\pi}\int _{0}^{\pi}e^{{z\mathop{\cos\/}\nolimits\theta}}\mathop{\cos\/}\nolimits\!\left(n\theta\right)d\theta.
10.32.4 \mathop{I_{{\nu}}\/}\nolimits\!\left(z\right)=\frac{1}{\pi}\int _{0}^{\pi}e^{{z\mathop{\cos\/}\nolimits\theta}}\mathop{\cos\/}\nolimits\!\left(\nu\theta\right)d\theta-\frac{\mathop{\sin\/}\nolimits\!\left(\nu\pi\right)}{\pi}\int _{0}^{\infty}e^{{-z\mathop{\cosh\/}\nolimits t-\nu t}}dt, |\mathop{\mathrm{ph}\/}\nolimits z|<\tfrac{1}{2}\pi.
10.32.5 \mathop{K_{{0}}\/}\nolimits\!\left(z\right)=-\frac{1}{\pi}\int _{0}^{\pi}e^{{\pm z\mathop{\cos\/}\nolimits\theta}}\left(\EulerConstant+\mathop{\ln\/}\nolimits\!\left(2z(\mathop{\sin\/}\nolimits\theta)^{2}\right)\right)d\theta.
10.32.6 \mathop{K_{{0}}\/}\nolimits\!\left(x\right)=\int _{0}^{\infty}\mathop{\cos\/}\nolimits\!\left(x\mathop{\sinh\/}\nolimits t\right)dt=\int _{0}^{\infty}\frac{\mathop{\cos\/}\nolimits\!\left(xt\right)}{\sqrt{t^{2}+1}}dt, x>0.
10.32.7 \mathop{K_{{\nu}}\/}\nolimits\!\left(x\right)=\mathop{\sec\/}\nolimits\!\left(\tfrac{1}{2}\nu\pi\right)\int _{0}^{\infty}\mathop{\cos\/}\nolimits\!\left(x\mathop{\sinh\/}\nolimits t\right)\mathop{\cosh\/}\nolimits\!\left(\nu t\right)dt=\mathop{\csc\/}\nolimits\!\left(\tfrac{1}{2}\nu\pi\right)\int _{0}^{\infty}\mathop{\sin\/}\nolimits\!\left(x\mathop{\sinh\/}\nolimits t\right)\mathop{\sinh\/}\nolimits\!\left(\nu t\right)dt, |\realpart{\nu}|<1, x>0.
10.32.8 \mathop{K_{{\nu}}\/}\nolimits\!\left(z\right)=\frac{\pi^{{\frac{1}{2}}}(\frac{1}{2}z)^{\nu}}{\mathop{\Gamma\/}\nolimits\!\left(\nu+\frac{1}{2}\right)}\int _{0}^{\infty}e^{{-z\mathop{\cosh\/}\nolimits t}}(\mathop{\sinh\/}\nolimits t)^{{2\nu}}dt=\frac{\pi^{{\frac{1}{2}}}(\frac{1}{2}z)^{\nu}}{\mathop{\Gamma\/}\nolimits\!\left(\nu+\frac{1}{2}\right)}\int _{1}^{\infty}e^{{-zt}}(t^{2}-1)^{{\nu-\frac{1}{2}}}dt, \realpart{\nu}>-\tfrac{1}{2}, |\mathop{\mathrm{ph}\/}\nolimits z|<\tfrac{1}{2}\pi.
10.32.9 \mathop{K_{{\nu}}\/}\nolimits\!\left(z\right)=\int _{0}^{\infty}e^{{-z\mathop{\cosh\/}\nolimits t}}\mathop{\cosh\/}\nolimits\!\left(\nu t\right)dt, |\mathop{\mathrm{ph}\/}\nolimits z|<\tfrac{1}{2}\pi.
10.32.10 \mathop{K_{{\nu}}\/}\nolimits\!\left(z\right)=\tfrac{1}{2}(\tfrac{1}{2}z)^{\nu}\int _{0}^{\infty}\mathop{\exp\/}\nolimits\left(-t-\frac{z^{2}}{4t}\right)\frac{dt}{t^{{\nu+1}}}, |\mathop{\mathrm{ph}\/}\nolimits z|<\tfrac{1}{4}\pi.

§10.32(iii) Products

Mellin–Barnes Type

For similar integrals for \mathop{J_{{\nu}}\/}\nolimits\!\left(z\right)\mathop{K_{{\nu}}\/}\nolimits\!\left(z\right) and \mathop{I_{{\nu}}\/}\nolimits\!\left(z\right)\mathop{K_{{\nu}}\/}\nolimits\!\left(z\right) see Paris and Kaminski (2001, p. 116).

§10.32(iv) Compendia

For collections of integral representations of modified Bessel functions, or products of modified Bessel functions, see Erdélyi et al. (1953b, §§7.3, 7.12, and 7.14.2), Erdélyi et al. (1954a, pp. 48–60, 105–115, 276–285, and 357–359), Gröbner and Hofreiter (1950, pp. 193–194), Magnus et al. (1966, §3.7), Marichev (1983, pp. 191–216), and Watson (1944, Chapters 6, 12, and 13).