Chapter 2: Problem 4
Find the Taylor series solution about \(x, y=0\) of the initial value problem \(u_{y}=\sin u_{x}, u(x, 0)=\pi x / 4\)
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Chapter 2: Problem 4
Find the Taylor series solution about \(x, y=0\) of the initial value problem \(u_{y}=\sin u_{x}, u(x, 0)=\pi x / 4\)
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Find the Taylor series solution about \(x, y=0\) of the initial value problem \(u_{y}=\sin u_{x}, u(x, 0)=\pi x / 4\)
Regularity of u defined by (60): (a) If \(f(x) \in L^{1}(\mathbf{R})\) has compact support, show that (60) defines a continuous weak solution of \(u^{\prime \prime}=f(x)\). (b) If, in addition to (a), \(f(x)\) is a bounded function on \(\mathbf{R}\), show \(u \in\) \(C^{1}(\mathbf{R})\), and \(u^{\prime}(x)=\frac{1}{2}\left(\int_{-\infty}^{x} f(y) d y-\int_{x}^{\infty} f(y) d y\right)\). (c) If, in addition to (a), \(f(x)\) is continuous, show that \(u\) is in fact a classical solution: \(u \in C^{2}(\mathbf{R})\) with \(u^{\prime \prime}=f\).
Show that the minimal surface equation \(\left(1+u_{y}^{2}\right) u_{x x}-2 u_{x} u_{y} u_{x y}+(1+\) \(\left.u_{x}^{2}\right) u_{y y}=0\) is everywhere elliptic.
. If \(a u_{x x}+2 b u_{x y}+c u_{y y}=d\) is elliptic (i.e., \(a c-b^{2}>0\) ), let \(W=\sqrt{a c-b^{2}}\). Show that solutions \(\mu, \eta\) of the Beltrami equations $$ \mu_{x}=\frac{b \eta_{x}+c \eta_{y}}{W} \quad \mu_{y}=-\frac{a \eta_{x}+b \eta_{y}}{W} $$ provide new coordinates transforming (7) to the form (14). [Note that \(\mu(x, y)=\int_{\gamma} \mu_{x} d x+\mu_{y} d y\), where \(\gamma\) is a path joining \((x, y)\) and a fixed point \(p_{0}\); path independence is provided by the Beltrami equations.]
Find the solution of the initial value problem \(u_{y y}=u_{x x}+u, u(x, 0)=e^{x}\), \(u_{y}(x, 0)=0\) in the form of power series expansion with respect to \(y\) [i.e., \(\left.\sum_{0}^{\infty} a_{n}(x) y^{n}\right]\). (Note: This is not a Taylor series.)
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