# how to fix error message Invalid expression as When calling a function or indexing a variable, use parentheses. Otherwise, check for mismatched delimiters.

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RITIKA Jaiswal on 13 Apr 2023
Commented: RITIKA Jaiswal on 13 Apr 2023
% Define the parameters
n = 25; % number of state variables
vz = 0.5 * ones(1, n); % vz_i values (constant)
rho = 0.2 * ones(1, n); % rho_alpha_i values (constant)
T = 500 * ones(1, n); % T_i values (constant)
Dr_alpha_i = 0.0045 * ones(n, 6); % D_r,alpha_i values (constant)
% Set the initial condition x0
x0 = zeros(n, 1);
% Set the time grid for integration
tspan = [0, 10]; % example: integrate from t=0 to t=10
% Set options for ode15s solver
opts = odeset('RelTol', 1e-6, 'AbsTol', 1e-9);
% Solve the system of equations using ode15s
[t, sol] = ode15s(@dxdt, tspan, x0, opts);
% Extract the state variables from the solution
x = sol(:, 1:n);
% Plot the results
figure;
plot(t, x);
xlabel('Time');
ylabel('State Variables');
legend('x_1', 'x_2', 'x_3', ... (list all the state variables), 'x_n');
title('State Variables vs. Time');
Invalid expression. When calling a function or indexing a variable, use parentheses. Otherwise, check for mismatched delimiters.
% Define the inputs u1(t) and u2(t)
function u1_val = u1(t)
% Define the input u1(t) as a constant value
u1_val = 650;
end
function u2_val = u2(t)
% Define the input u2(t) as a constant value
u2_val = 650;
end
% Define the system dynamics
function x_dot = dxdt(t, x)
% Extract state variables from x
x_i = x(1:n);
% Compute A1(x(t)) and B1(x(t))
A1 = diag(-vz.^(n+0.5));
B1 = Dr_alpha_i;
% Compute B2 and f(x(t))
B2 = diag(zeros(1, n));
f = [(-vz(1:end-1).^(n+0.5)).*(rho.^(n+0.5)), (-vz(1:end-1).^(n+0.5)).*(T.^(n+0.5))];
% Compute x_dot
u1_val = u1(t); % Call u1(t) function handle with parentheses
u2_val = u2(t); % Call u2(t) function handle with parentheses
x_dot = A1*x_i + B1*u1_val + B2*u2_val + f';
end
after running thecode i am geting error message even how can i fixthe error?
Error message:
Invalid expression. When calling a function or indexing a variable, use parentheses. Otherwise, check for mismatched delimiters.
Dyuman Joshi on 13 Apr 2023
1 - You need to define the variables inside the ODE function or either pass them as input arguements. I have edited the code with the former option.
2 - There's a dimension mis-match while defining f (as the error states as well). Since I do not know what you are trying to do, I can not offer any suggestion.
n=25;
% Set the initial condition x0
x0 = zeros(n, 1);
% Set the time grid for integration
tspan = [0, 10]; % example: integrate from t=0 to t=10
% Set options for ode15s solver
opts = odeset('RelTol', 1e-6, 'AbsTol', 1e-9);
% Solve the system of equations using ode15s
[t, sol] = ode15s(@(t,y) dxdt(t,y,n), tspan, x0, opts);
Arrays have incompatible sizes for this operation.

Error in solution>dxdt (line 50)
f = [(-vz(1:end-1).^(n+0.5)).*(rho.^(n+0.5)), (-vz(1:end-1).^(n+0.5)).*(T.^(n+0.5))];

Error in solution>@(t,y)dxdt(t,y,n) (line 9)
[t, sol] = ode15s(@(t,y) dxdt(t,y,n), tspan, x0, opts);

Error in odearguments (line 92)
f0 = ode(t0,y0,args{:}); % ODE15I sets args{1} to yp0.

Error in ode15s (line 153)
odearguments(odeIsFuncHandle, odeTreatAsMFile, solver_name, ode, tspan, y0, options, varargin);
% Extract the state variables from the solution
x = sol(:, 1:n);
% Plot the results
figure;
plot(t, x);
xlabel('Time');
ylabel('State Variables');
%legend('x_1', 'x_2', 'x_3', ... (list all the state variables), 'x_n');
title('State Variables vs. Time');
% Define the inputs u1(t) and u2(t)
function u1_val = u1(t)
% Define the input u1(t) as a constant value
u1_val = 650;
end
function u2_val = u2(t)
% Define the input u2(t) as a constant value
u2_val = 650;
end
% Define the system dynamics
function x_dot = dxdt(t, x, n)
rho = 0.2 * ones(1, n); % rho_alpha_i values (constant)
T = 500 * ones(1, n); % T_i values (constant)
Dr_alpha_i = 0.0045 * ones(n, 6); % D_r,alpha_i values (constant)
% Extract state variables from x
x_i = x(1:n);
vz = 0.5 * ones(1, n); % vz_i values (constant)
% Compute A1(x(t)) and B1(x(t))
A1 = diag(-vz.^(n+0.5));
B1 = Dr_alpha_i;
% Compute B2 and f(x(t))
B2 = diag(zeros(1, n));
f = [(-vz(1:end-1).^(n+0.5)).*(rho.^(n+0.5)); (-vz(1:end-1).^(n+0.5)).*(T.^(n+0.5))];
% Compute x_dot
u1_val = u1(t); % Call u1(t) function handle with parentheses
u2_val = u2(t); % Call u2(t) function handle with parentheses
x_dot = A1*x_i + B1*u1_val + B2*u2_val + f';
end
RITIKA Jaiswal on 13 Apr 2023
I am trying to solve ode derived by using finite volume method.

Cris LaPierre on 13 Apr 2023
You need to properly end the line that creates your legend.
%this
legend('x_1', 'x_2', 'x_3', ... (list all the state variables), 'x_n');
% should be this
legend('x_1', 'x_2', 'x_3') %, ... (list all the state variables), 'x_n');

Jon on 13 Apr 2023
The specific error you get is for line 22 where you have
legend('x_1', 'x_2', 'x_3', ... (list all the state variables), 'x_n');
You never close the parenthesis, you just have a ... followed by some texts. MATLAB is telling you that you need to have a right hand parenthesis to close the expression. Once you fix this your code has additional bugs. If you can't resolve these please tell us where you are stuck.
RITIKA Jaiswal on 13 Apr 2023
@Jon Thankyou so much for your help .yes the code has additional bugs too. following are the errors which i am getting after corecting the code.
Error in implo>dxdt (line 45)
x_i = x(1:n);
Error in odearguments (line 90)
f0 = feval(ode,t0,y0,args{:}); % ODE15I sets args{1} to yp0.
Error in ode15s (line 152)
odearguments(FcnHandlesUsed, solver_name, ode, tspan, y0, options, varargin);
Error in implo (line 18)
[t, sol] = ode15s(@dxdt, tspan, x0, opts);

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