ode45功能错误

Question

I'm trying to simulate nonlinear vehicle braking system with ode45.

I take a short time to learning MATLAB. then, I don't know why error occur.

It would be very appreciated if you could point out errors, and tell me how to solve.

code 1. main script code 2. function code 3. errors

    clear;
    global m f Jw rw Fz Cd p A bw fw Nw g uw seta Te Tb T p0
    x = [0 0.025 0.05 0.1 0.125 0.15 0.175 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1]
    y = [0 0.225 0.45 0.65 0.685 0.705 0.69 0.68 0.65 0.635 0.63 0.6275 0.625 0.6225 0.62 0.6175 0.615 0.6125 0.610 0.6075 0.6050 0.6 0.5975 0.5950]
    %plot(x,y)
    p0=polyfit(x,y,6)
    %y=polyval(p,x)

    m = 1400; f = 0.01; Jw = 0.65; rw = 0.31; Fz = 3560.0; Cd = 0.5; p = 1.202; A = 1.95;
    bw = 0.0; fw = 0.0; Nw = 4; g = 9.81; uw = 0.0; seta = 0.0; Te = 0.0; Tb = 1000.0; T = Te - Tb;



[t,i] = ode45(@dott,[0.0 1.0],[20 20]);
plot(t,i);
axis([0 1 0 20]);
legend('x1','x2');

function xdot = dott(t,x)
global m f Jw rw Fz Cd p A Nw Te Tb p0
X = [0 0.025 0.05 0.1 0.125 0.15 0.175 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1];
Y = [0 0.225 0.45 0.65 0.685 0.705 0.69 0.68 0.65 0.635 0.63 0.6275 0.625 0.6225 0.62 0.6175 0.615 0.6125 0.610 0.6075 0.6050 0.6 0.5975 0.5950];
%UNTITLED2 Summary of this function goes here
%Detailed explanation goes here
xdot = zeros(2,1);
Y=p0(1,1)*((x(2)-x(1))/x(1))^6+p0(1,2)*((x(2)-x(1))/x(1))^5+p0(1,3)*((x(2)-x(1))/x(1))^4+p0(1,4)*((x(2)-x(1))/x(1))^3+p0(1,5)*((x(2)-x(1))/x(1))^2+p0(1,6)*((x(2)-x(1))/x(1))^1+p0(1,1)*((x(2)-x(1))/x(1));
xdot(1)=(-0.5*p*Cd*A(x(2)/(1+Y)*rw)*(x(2)/(1+Y)*rw)-f*m+Nw*Y*Fz)/(rw*m); 
xdot(2)=(Te-Tb-rw*Y*Fz)/Jw;

end

??? Subscript indices must either be real positive integers or logicals.

Error in ==> dott at 9
xdot(1)=(-0.5*p*Cd*A(x(2)/(1+Y)*rw)*(x(2)/(1+Y)*rw)-f*m+Nw*X*Fz)/(rw*m);

Error in ==> odearguments at 98
f0 = feval(ode,t0,y0,args{:});   % ODE15I sets args{1} to yp0.

Error in ==> ode45 at 172
[neq, tspan, ntspan, next, t0, tfinal, tdir, y0, f0, odeArgs, odeFcn, ...

Error in ==> a at 14
[t,i] = ode45(@dott,[0.0 1.0],[20 20]);

Answer 1

I'm pretty sure your error is in this statement:

A(x(2)/(1+Y)*rw)

The way you write it, you're trying to use x(2)/(1+Y)*rw as an index to the scalar A . I guess you want to multiply is this way:

... A * (x(2) / (1 + Y) * rw) ...

To make the code more readable:

1. Use spaces. A long compact line is really hard to read.
2. Split long lines into several using three dots ...

Something like this is easier to read in my opinion:

Y = p0(1,1) * ((x(2) - x(1)) / x(1))^6 + p0(1,2) * ...
    ((x(2) - x(1)) / x(1))^5 + p0(1,3) * ((x(2) - x(1)) / x(1))^4 ...
    + p0(1,4) * ((x(2) - x(1)) / x(1))^3 + p0(1,5) * ((x(2) - x(1)) / ...
    x(1))^2 + p0(1,6) * ((x(2) - x(1)) / x(1))^1 + p0(1,1) * ...
    ((x(2) - x(1)) / x(1));