Undefined function 'int' for input arguments of type 'char'.

Hi Guys

this code gives me this error when I tried to change it a little

Any solutions?

syms n t ;
n=50;                      
t=linspace(-5,5,1000);          
T=max(t);                       
wo=(2*pi)/T;                   
for k=1:n
    ao= (1/T).*(int('1',t,0,t));
    an= (2/T).*(int('1*cos(n*wo*t)',t,0,t))
    bn= (2/T).*(int('1*sin(n*wo*t)',t,0,t))
    f=ao+(an.*cos(k.*wo.*t))+(bn.*sin(k.*wo.*t));
end
figure(1);clf(1)
plot(t,f)
xlabel('Time')
ylabel('Amplitude')
title('Fourier sawtooth Trasnform')

[Stephen23]

Newer MATLAB versions only accept symbolic inputs to int, as the documentation clearly shows:

https://www.mathworks.com/help/symbolic/int.html#inputarg_expr

What do you expect a character input to do? What MATLAB version are you using?

[Walter Roberson]

Character input is still supported, though no longer documented.

Answer 1

[Walter Roberson]

You have

syms n t ;

which is equivalent to

n = sym('n');
t = sym('t');

which make connections between those variables in the MATLAB workspace and symbolic variables with those names inside the symbolic engine.

You have

n=50;                      
t=linspace(-5,5,1000);

This breaks the connection between the variables in the MATLAB workspace and the variables in the symbolic engine, because you wrote over variables with the same names.

You have

     ao= (1/T).*(int('1',t,0,t));

You replaced t with a numeric variable, so this is

   int('1', NUMERIC_VECTOR, 0, NUMERIC_VECTOR)

None of the parameters are object-oriented objects, so the first parameter is used as the data type to search for a matching method. There is no method int for character vectors, so you get a failure.

If you had used

       ao= (1/T).*(int(sym('1'),t,0,t));

then since there was an object-oriented parameter, the int method for that object would be looked up and found, so symbolic int would be called. However, this case would be

int(SYMBOL, NUMERIC_VECTOR, 0, NUMERIC_VECTOR)

and symbolic int cannot have a numeric vector as it second argument.

So what you should have done is not re-used the variable 't' between the syms t and the t = linspace(...) . Use different variable names for the two, and use the appropriate variable names in the appropriate positions in the int() call.

If syms t was still in effect, then the call would be

int(CHARACTER_VECTOR, SYMBOL, 0, SYMBOL)

which would invoke symbolic int, which would automatically transform it to equivalent to

int(sym(CHARACTER_VECTOR), SYMBOL, 0, SYMBOL)

and do the integration. Perhaps

syms n t ;
n=50;                      
trange=linspace(-5,5,1000);          
T=max(trange);                       
wo=(2*pi)/T;                   
for k=1:n
    thist = trange(k);
    ao= (1/T).*(int('1',t,0,thist));
    an= (2/T).*(int('1*cos(n*wo*t)',t,0,thist))
    bn= (2/T).*(int('1*sin(n*wo*t)',t,0,thist))
    f(k) = ao+(an.*cos(k.*wo.*thist))+(bn.*sin(k.*wo.*thist));
end
figure(1);clf(1)
plot(t,f)
xlabel('Time')
ylabel('Amplitude')
title('Fourier sawtooth Trasnform')

[Rana 55]

I tried what you said but it gives me another error (A numeric or double convertible argument is expected)

[Walter Roberson]

syms n t ;
n=50;                      
trange=linspace(-5,5,n);          
T=max(trange);                       
wo=(2*pi)/T;                   
for k=1:n
    thist = trange(k);
    ao= (1/T).*(int(sym(1), t, 0, thist));
    an= (2/T).*(int(1*cos(n*wo*t), t, 0, thist));
    bn= (2/T).*(int(1*sin(n*wo*t), t, 0, thist));
    f(k) = ao+(an.*cos(k.*wo.*thist))+(bn.*sin(k.*wo.*thist));
end
figure(1);clf(1)
plot(trange,f)
xlabel('Time')
ylabel('Amplitude')
title('Fourier sawtooth Trasnform')