Undefined function or variable x when using ode45?

I'm trying to use ode45 to solve a fairly complicated system of first order odes. When I run the script it says there is an undefined variable 'x' in the function.

Code:

function dx = differentials(t,x)
%Initialize vector
dx = zeros(1:5);
%Define New Variables
D = c*(exp(2*sigma_l*Lc*(f2l*x(2)-f1l*x(1)))-1);
Rp = Pin*((1-exp(sigma_p*Lc*(f2p*x(2)-f1p*x(1))))/(h*freq_p*Lc*Ap));
rc = (-c*ln(1-Toc))/(2*Lr);
%Define differential equations
dx(1) = -Rp + (D*x(5))/(2*Lc)+W21*x(2)+W31*x(3)+W41*x(4)+Cup*(x(2))^2;
dx(2) = Rp - (D*x(5))/(2*Lc)-W21*x(2)+W32*x(3)+W42*x(4)-2*Cup*(x(2))^2;
dx(3) = -W31*x(3)-W32*x(3)+W43*x(4);
dx(4) = -W41*x(4)-W42*x(4)-W43*x(4)+Cup*(x(2))^2;
dx(5) = (D*x(5))/(2*Lc)-rc*x(5)+phi_sp;
end

%Solve Equations
[T,X] = ode45(@differentials,[0,t_length],N0);

All constants mentioned have been defined already. I've checked that they are not the problem. The error comes in at the first mention of x in the function. What am I doing wrong?

Answer 1

[Jan]

"zeros(1:5)" does not do what you expect, because you want "zeros(5, 1)".

Please copy the complete error message, when you discuss a problem in the forum. There might be important details in the message.

I guess, that you call the function differentials anywhere and forgot the "@". The debugger or the complete error message will reveal the crashing line. Type this in the command window:

dbstop if error

Then run the program again and locate the problem.

I do not understand where the values of c, sigma_L, Lc, f21 etc should come from. Where did you define them? In the shown code the missing definition will cause further errors.