# incorrect number or types of inputs or outputs for function 'int'

138 views (last 30 days)
Gary on 29 Mar 2023
Commented: Gary on 31 Mar 2023
When I put this code with int function, it always says in red: Wrong type or number in function int. Tried to change units, tried all which I could do.
% Define the parameters of the signal
A = 1; % Amplitude
T_0 = 4*pi; % Period
t = linspace(0, T_0, 1000); % Time vector
% Generate the signal
y = A*cos(4*pi*t/T_0);
% Calculate the power of the signal using integration
power = (1/T_0) * int((y).^2, t(1), t(end));
Incorrect number or types of inputs or outputs for function 'int'.
% Plot the signal
plot(t, y);
xlabel("Time (s)");
ylabel("Amplitude");
title("A*cos(4*pi*t/T_0)");
% Display the signal power
disp(['Signal power = ' num2str(power)]);

Torsten on 30 Mar 2023
Moved: Torsten on 30 Mar 2023
% Define the parameters of the signal
A = 1; % Amplitude
T_0 = 4*pi; % Period
syms t
% Generate the signal
y = A*cos(4*pi*t/T_0);
% Calculate the power of the signal using integration
power = (1/T_0) * int(y^2)
power =
power = matlabFunction(power)
power = function_handle with value:
@(t)t.*3.978873577297384e-2+sin(t.*2.0).*1.989436788648692e-2
y = matlabFunction(y)
y = function_handle with value:
@(t)cos(t)
t_num = linspace(0, T_0, 1000); % Time vector
y_num = y(t_num);
% Plot the signal
plot(t_num, y_num);
xlabel("Time (s)");
ylabel("Amplitude");
title("A*cos(4*pi*t/T_0)");
% Display the signal power
power_num = power(t_num(end))-power(t_num(1));
disp(['Signal power = ' num2str(power_num)]);
Signal power = 0.5

Alan Stevens on 29 Mar 2023
Edited: Alan Stevens on 29 Mar 2023
power = (1/T_0) * trapz(t,y.^2);
Edited - Walter is correct.
Steven Lord on 30 Mar 2023
The int function to perform integration is only defined for symbolic inputs, not numeric inputs. So this works:
syms x
int(x^2)
ans =
but this doesn't.
y = (1:10).^2;
int(y)
Incorrect number or types of inputs or outputs for function 'int'.
In your code y is a vector of values not a symbolic expression.
Gary on 31 Mar 2023
Thank you for your grateful, thoughtful words!!

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