/// <summary>
/// computes integral by the integrand, initial value and difference.
/// </summary>
/// <param name="delayedIntegrand">delayed integrand</param>
/// <param name="initialValue">initial value</param>
/// <param name="dt">difference</param>
/// <returns></returns>
static Stream <double> Integral(Delayed <Stream <double> > delayedIntegrand, double initialValue, double dt)
{
Stream <double> inte = null;
inte = Cons(initialValue, () => AddStream(delayedIntegrand.Force().Select(x => x * dt), inte));
return(inte);
}
