i could not fix the error part !

% Solution of second-order differential equation

% The function diff2(x,y) is created to evaluate the diff. equation

% the name of the m-file is diff2.m

% the function is defined as:

%

function xdot = diff2(t,x)

is = 2;

c = 50e-6; L = 1/32; r = 10;

k1 = 1/c ; % 1/C

k2 = 1/L ; % 1/L

k3 = 1/(r*c); % 1/RC

xdot(1) = k2*x(2);

xdot(2) = k1*is - k1*x(1) - k3*x(2);

end

% solution of second-order differential equation

% the function diff2(x,y) is created to evaluate

% the differential equation

% the name of m-file is diff2.m

%

% Transient analysis of RLC circuit using ode function

% numerical solution

t0 = 0;

tf = 30e-3;

x0 = [0 20]; % Initial conditions

[t,x] = ode23('diff2',t0,tf,x0);

% Second column of matrix x represent capacitor voltage

subplot(211), plot(t,x(:,2))

xlabel('Time, s'), ylabel('Capacitor voltage, V')

text(0.01, 7, 'State Variable Approach')

% Transient analysis of RLC circuit from Example 5.5

t2 =0:1e-3:30e-3;

vt = -6.667*exp(-1600*t2) + 26.667*exp(-400*t2);

subplot(212), plot(t2,vt)

xlabel('Time, s'), ylabel('Capacitor voltage, V')

text(0.01, 4.5, 'Results from Example 5.5')

this is the codes of my work... i think in the line 26 something going wrong.... could you help me the fix this ?

Answer 1

[Star Strider]

The problems were that the ode23 call has to be:

[t,x] = ode23(@diff2,[t0,tf],x0);

so it refers to ‘diff2’ correctly as a function handle, and the ‘tspan’ variables are now a (1x2) vector.

and the function must be at the end of the script. The function also has to return a column vector, so I fixed that problem with:

xdot(1,:) = k2*x(2);

xdot(2,:) = k1*is - k1*x(1) - k3*x(2);

It now runs without error.

% solution of second-order differential equation
% the function diff2(x,y) is created to evaluate
% the differential equation
% the name of m-file is diff2.m
%
% Transient analysis of RLC circuit using ode function
% numerical solution
t0 = 0;
tf = 30e-3;
x0 = [0 20]; % Initial conditions
[t,x] = ode23(@diff2,[t0,tf],x0);
% Second column of matrix x represent capacitor voltage
subplot(211), plot(t,x(:,2))
xlabel('Time, s'), ylabel('Capacitor voltage, V')
text(0.01, 7, 'State Variable Approach')
% Transient analysis of RLC circuit from Example 5.5
t2 =0:1e-3:30e-3;
vt = -6.667*exp(-1600*t2) + 26.667*exp(-400*t2);
subplot(212), plot(t2,vt)
xlabel('Time, s'), ylabel('Capacitor voltage, V')
text(0.01, 4.5, 'Results from Example 5.5') 

function xdot = diff2(t,x)
is = 2;
c = 50e-6; L = 1/32; r = 10;
k1 = 1/c ; % 1/C
k2 = 1/L ; % 1/L
k3 = 1/(r*c); % 1/RC
xdot(1,:) = k2*x(2);
xdot(2,:) = k1*is - k1*x(1) - k3*x(2);
end 

.