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Mathematical Methods for Physics and Engineering - Matematica.NET

Mathematical Methods for Physics and Engineering - Matematica.NET

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25.8 APPROXIMATIONS TO INTEGRALS(a)(b)π/4β(c)√ π∫ ∞Figure 25.13 Amplitude–phase diagrams <strong>for</strong> the integral−∞ exp(−z2 ) dzusing different contours in the complex z-plane. (a) Using the real axis, as inthe steepest descents method. (b) Using the level line z = u exp(− 1 iπ) that4passes through the saddle point, as in the stationary phase method. (c) Usinga path that makes a positive angle β (< π/4) with the z-axis.The final curve, 25.13(c), shows the amplitude-phase diagram corresponding toan integration path that is along a line making a positive angle β (0

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