Matlab take a long time for evaluation

When I evaluate the program (given below), matlab take a long time to evaluate this program. How to get rid off from this problem?

syms x

D=0.1;

k1=-0.5; c1=1; a=1; b=2; 

C=1+c1*exp(k1*x);

u0=diff(log(C),x);

u0=inline(u0);

x=[-50:D:50];

u0=u0(x);

options=odeset('RelTol',1e-4,'AbsTol',1e-8);

[t u]=ode45(@dydt, [0:D^3:40], u0, options);

T=t;

X=[-50:D:50];

[t,x]=meshgrid(T,X);

u=u';

t=t(:,1:8000:40001);

x=x(:,1:8000:40001);

U=u(:,1:8000:40001);

plot3(x,t,U,'.')

axis([-50 50 0 40 -0.5 0])

[Jan]

What does "a long time" mean exactly? Too many seconds or weeks? You did not post the code for |dydt|. Did you check if the ODE is stiff? Then ODE45 is a bad choice. The absolute tolerance of 1e-8 might be too small for an efficient integration. BY the way, see <http: how to format code in the forum>. There is no need for square brackets around vectors, this is sufficient already: |X=-50:D:50;|. </http:>