n = 51;
std = 0.1;
x1 = 1.27;
x2 = 2.04;
x3 = 0.3 * rand ( n, 1 );
lambda1 = 27.0;
lambda2 = 8.0;
t = ( linspace ( 0.0, 0.4, n ) )';
phi = x1 * exp ( - lambda1 * t ) + x2 * exp ( - lambda2 * t ) + x3;
plot ( t, phi, 'bo' );
grid on