function [ uex, uexx ] = exact ( x )
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%  [ uex, uexx ] = exact ( x )
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%  EXACT returns the value of the exact solution U and its derivative dU/dX at X.
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%  X(*) is the point or points of evaluation.
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%  UEX(*) is the value of U at X.
%  UEXX(*) is the value of dU/dX at X.
%
n = length ( x );

uex(1:n) = sin ( pi * x(1:n) );
uexx(1:n) = pi * cos ( pi * x(1:n) );