Changing parameters while simulation

The following code is a part of my program :

a = [1 -1.98 1.284 -0.272];
b = [0 5 2 6];
th = poly2th(a,b)
u = rand(1000,1);
y = idsim(u,th);
% now i want to change the parameters  say at 300th sample; so
 a= [ 1 -2 1 -0.4];
 b = [0 5 2 6];

So my question is ; I want my values of output y i.e y (1 :299 ) should be from unchanged parameters and y (300 :1000 ) should be from parameters after i change.

those values of y should be concatenated in the column vector of y (1:1000)

So can anyone help me this..?

Answer 1

[Walter Roberson]

th1 = poly2th(a, b);
u1 = rand(1000, 1);
y1 = idsim(u1, th1);

y2 = [reshape(y(1:299),[], 1); reshape(y1(300:1000), [], 1)];

[Sai kasyap]

Thanks again walter roberson!