Error coming as Not enough input arguments

function dx = invpen(t,x)

M = 3;

m = 0.4;

I = 1.5;

g = 9.8;

b = 1;

U = 0;

dx=zeros(4,1);

dx(1)=x(2);

dx(2)=((-g*m*sin(x(3))*cos(x(3))) + (m*l*(x(4))^2*sin(x(3))) + (m*b*x(4)*cos(x(3))) + U)/(M+(1-(cos(x(3))*cos(x(3))))*m);

dx(3)=x(4);

dx(4)=(((M+m)*((b*x(4))-(g*sin(x(3))))) + (m*l*(x(4))^2^sin(x(3))+cos(x(3)))+ (U*cos(x(3))))/(l*((m*cos(x(3))*cos(x(3)))-M-m));

end

[Karan Kannoujiya]

Hi Arjun,

Could you please send how you calling the function and the value of x and t you are passing in function.

[Arjun Gupta]

clc

clear all

close all

L = 1.5;

t = 0:0.01:10;

x0 = [0.5 0 pi/2 0];

[t x]=ode45('invpend',t,x0);

figure

subplot(2,2,1)

plot(t,x(:,1))

xlabel('Time(sec)'), ylabel('m')

title('x')

subplot(2,2,2)

plot(t,x(:,2))

xlabel('Time(sec)'), ylabel('m/s')

title('x^{.}')

subplot(2,2,3)

plot(t,x(:,3))

xlabel('Time(sec)'), ylabel('rad')

title('\theta')

subplot(2,2,4)

plot(t,x(:,4))

xlabel('Time(sec)'), ylabel('rad/sec')

title('\theta^{.}')

X0 = 0;

Y0 = 0;

for i = 1:length(t)

Xc = x(i,1);

Xp = x(i,1) + L * sin(pi - x(i,3));

Yp = L * cos(pi - x(i,3));

figure(2)

plot([-3 5], [0 0], 'linewidth', 6, 'color', 'g');

axis([-4 6 -4 4]);

line([Xc Xp], [Y0, Yp], 'linewidth', 2, 'color', 'b');

hold on

plot(Xc, Y0, 's', 'markersize', 30, 'markerfacecolor', 'y');

plot(Xp, Yp, 'o', 'markersize', 15, 'markerfacecolor', 'r');

hold off

end

Answer 1

[Raghav]

Hi @Arjun Gupta,

There are a few problems in this function.

First input argument 't' is not used anywhere in the function, so you can remove it from input argument list to remove this warning.

Second, the variable 'l' used in the calculation of dx(2) and dx(4)is not defined, also the variable 'ɪ' you defined is not used anywhere in the function, so I guess in the original formula, there was 'ɪ' instead of 'l' like:

dx(2)=((-g*m*sin(x(3))*cos(x(3))) + (m*I*(x(4))^2*sin(x(3))) + (m*b*x(4)*cos(x(3))) + U)/(M+(1-(cos(x(3))*cos(x(3))))*m);

and

dx(4)=(((M+m)*((b*x(4))-(g*sin(x(3))))) + (m*I*(x(4))^2^sin(x(3))+cos(x(3)))+ (U*cos(x(3))))/(I*((m*cos(x(3))*cos(x(3)))-M-m));

If you still face the error- "Not enough input arguments", call the function "invpen" with proper x, x should be an array of size atleast 4.