inputsize=1559;
m=1;
k=1;
h=0.02;
numberTDs=5;
%Import data and zero time and acceleration matrices
data=importdata('EarthquakeData.xlsx');
[ii,jj]=size(data);
acc=zeros(1,inputsize);
%T=zeros(1,inputsize);
T=0:h:(inputsize-1)*h;
n=1;
for i=1:ii
for j=1:jj
acc(1,n)=data(i,j);
n=n+1;
if n>inputsize
break
end
end
end
y0 = [0,0];
C1 = (4*pi*xi/TD);
C2 = (2*pi/TD)^2;
[t, Y] = ode45( @(t,y) goodfunction1(t, y, acc, C1, C2), T, y0);
%%%FUNCTION
function ydot = goodfunction1(t, y, acc, C1, C2 )
a = interp1(T, acc, t);
ydot = [y(2); -C1*y(2) - C2*y(1) - a];
end
However... your use of interp1 to interpolate tells us that your equations are at best piecewise continuous. That is not good enough for any of the ode*() solvers. ode45() will probably detect the inconsistency in equations the first time a makes a non-linear change, and will spend a whole lot of time trying to narrow down the instability. This would be very slow if it works at all.
In any case in which your equation suddenly changes like this, you should be stopping the ode and starting again with another ode45 call using the boundary conditions returned by the previous one. ode45() cannot handle discontinuities in any derivative that it is working with (and probably not in two more beyond that.)
