ode45 issue: dimension mismatch

[Tweety]

Dear all,

For my first time, I am trying to solve a differential equation using
ode45. My code looks like this:

clear; clc;
t = linspace(0,400,401);
x0 = [0, 0];
function f = dx(x,t)
M = 2.933e-5;
m = 0.158;
n = 1.26;
dx = M*x^m(1-x)^n;
endfunction
[t,x] = ode45(@dx, t, x0);

The error I get is a dimension mismatch and I do not understand a
mismatch between which parameters.

Can this function be solved by ode45 at all or should I use a different
solver or bring the function to a different form? If so, which? I
appreciate any kind of information.

Thanks,
Jan