Although M is nonsingular, but the inv(M) is very complicated, and when put to the right side,it turns out to be abnormal output of some of the states stay zero. So I have to use the Mass option in the odeset.
And f(y) is so complicated a nonlinear equation that I can't draw it out in Simulink using small nonlinear blocks.So I have to use the s- function block.
So where to add the options in s-funtion block in Simulink? I looked up the docs of s-function but it seems that there is no guidance there for such a case, then how can I do? Is there anyway to convert the equation to another form?