Exercise 11.4, number 4 should be:
α = 2 , L = 20 {\displaystyle \alpha =2,L=20} , and
u ( x , 0 ) = { 0 , 0 < x ≤ 3 sin 2 π x , 3 < x ≤ 7 2 0 , 7 2 < x ≤ 20. {\displaystyle u(x,0)=\left\{{\begin{array}{lc}0,&0<x\leq 3\\\sin 2\pi x,&3<x\leq {\frac {7}{2}}\\0,&{\frac {7}{2}}<x\leq 20.\end{array}}\right.}
Return to errata.
