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F 1
D f.t n ; u n /;
D f.t nC1=2 ; u n C t
2
F 2
F 1 /;
D f.t nC1=2 ; u n C t
2
F 3
F 2 /;
F 4
D f.t nC1 ; u n C tF 3 /;
t
6
u nC1 D u n C
ŒF 1 C 2F 2 C 2F 3 C F 4 :
Implement this scheme and perform the experiments of (g) and (h) above. Try,
using experiments, to figure out the accuracy of this scheme.
(m) Consider the initial value problem
2.1 t/
" 2
u 0 .t / D
u
u .0/ D e 1=" 2 ;
where " is given. Show that the solution of this problem is given by
/ 2 :
u .t / D e . 1t
"
(n) Set " D 1=4: We want to compute the solution at time t D 1:1: Compare
the accuracy of all the schemes above (explicit Euler, implicit Euler, Crank-
Nicolson, Heun, and Runge-Kutta) for this problem. Say we want the absolute
error to be less than 10 5 : Make a ranking of the schemes based on how much
CPU time they need to achieve this accuracy.
 
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