How to reduce the running time using dsolve

Hello,

I would like to solve ode using dsolve function. It was mainly to analyse the system behavior by step input.

The equation that I want to solve looks like the following.. A*D4(y(t)) + B*D3(y(t)) + C*D2(y(t)) + D = E*D2(u(t)) + F*(D(u(t))) + G*(u(t))

which u(t) : Step function Boundary Condition : y(0) = 0, y(0.1) = 0, y(0.5) = 0, Dy(0) = 0

Details are attached as a m-file.

When I run this code in Matlab, it runs without end. Instead of u(t) as a step function (using heaviside), I have also tried u(t)= 1./(1+exp(-(t-1)/0.05)); as well but it was also running without an end.

Are there any suggestions that enables to solveo this equations?

I will be very glad to hear some tips..

Thanx for reading.