D'Alembert formula (source code)

= D'Alembert formula
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{wiki=D'Alembert's_formula}

The Cauchy problem $u_{tt}=c^2u_{xx}$ has
$$
u(x,t)=\frac{f(x-ct)+f(x+ct)}2+\frac1{2c}\int_{x-ct}^{x+ct}g(y)dy.
$$