need help in plotting curve

[navshinder]

hi,
I'm trying a dynamics problem and trying to plot the displacement with
respect to time function.  However I'm returned with an error message
"subscripts must be either integers 1 to (2^63)-1 or logicals
error: called from
    utvst at line 7 column 3"
which I'm not able to figure out
thanks

t = linspace(0,0.01,500);
x0 = 0.01;
xdot0 = 0.1;
m = 40;
k = 3500;
omega = sqrt(k/m);
ut = sum((x0.*cos(omega.*t))+((xdot0/omega)(sin(omega.*t))));
plot(ut,t)




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