Int function not working

Hi all, im relatively new to the whole MATLAB thing and was wondering why my below code isnt working and giving me the error:

Check for missing argument or incorrect argument data type in call to function 'int'.

Error in MME32 (line 17)

c0=(1/T)*int(f1,T/2,0)+(1/T)*int(f2,0,T/2)

My Code:

clear

t1=-pi:0.001:0;
t2=0:0.001:pi;
w=2;
T=(2*pi)/w;

f1=(4+t1)/2;
f2=(2-t2).*cos(2*t2);
hold on
plot(t1,f1)
plot(t2,f2)

c0=(1/T)*int(f1,-T/2,0)+(1/T)*int(f2,0,T/2)

i also have the line of code:

c(n)=(1/T)*int(@f1.*exp(-j*n*w*t1),T/2,0)+(1/T)*int(@f2.*exp(-j*n*w*t2,0,T/2)

that doesnt work either.

Thanks in advance!

[Jan]

Whenever you mention an error in the forum, post a copy of the complete error message. "Does not work" ist not clear enough to understand, what the problem is.

f1 is a numerical vector. Then "@f1" does not create symbolic expression and not a function handle also.

[Jai Harnas]

Okay, i will do that in future thank you

Answer 1

[Walter Roberson]

You have no symbolic variables or symbolic functions. int() is only used for symbolic expressions or symbolic functions.

For numeric integration, there are several routines, the main two of which are integral() and integral2(). However, for those you need function handles.

w=2;
T=(2*pi)/w;
f1 = @(t) (4+t)/2;
f2 = @(t) (2-t).*cos(2*t);
fplot(f1, [-T/2, 0]);
hold on
fplot(f2, [0, T/2]);

c0 = (1/T)*integral(f1,-T/2,0) + (1/T)*integral(f2,0,T/2)

c0 = 0.9628

[Jai Harnas]

Thank you this works perfectly! i did try something similar to this but had things around the wrong way and all messed up. Thank you !

Answer 2

[Jan]

See:

doc int

The 1st argument must be: symbolic expression | symbolic function | symbolic vector | symbolic matrix | symbolic number

You provide a numerical vector instead. Then trapz is the right tool for an integration.