Warning: Error updating FunctionLine using fplot

Hi all, Wondering why i am getting the warning: error updating FunctionLine warning when trying to plot from a series addition, below is code attached which all works apart from the "fplot(s, [-pi,pi])"

Thanks in advance!

clear
syms k

w=2; %angular frequency
T=(2*pi)/w; %working out the period
f1=@(t)(4+t)/2; %f(t)
f2=@(t) (2-t).*cos(2*t); %f(t)

hold on %plotting both functions within their intervals
fplot(f1,[-pi,0]);
fplot(f2,[0,pi]);

%labelling the axis
xlabel('Time (s)')
ylabel('Cosine Values')

%evaluating C0
c0=(1/T)*integral(f1,-T/2,0)+(1/T)*integral(f2,0,T/2);

%evaluating Cn values up to n=10 from n=1
for n = 1:10
    f3=@(t) ((4+t)/2).*exp(-1j*n*w*t);
    f4=@(t) ((2-t).*cos(2*t)).*exp(-1j*n*w*t);
    c(n)=(1/T)*integral(f3,-T/2,0)+(1/T)*integral(f4,0,T/2);
    n=+1;
end 

%series addition for k=-10:10
s=@(t) symsum(c(k).*exp(1j*k*w*t),-10,10);

fplot(s,[-pi,pi])

%evaluating the average energy of the signal
f5=@(t) abs((4+t)/2).^2;
f6=@(t) abs((2-t).*cos(2*t)).^2;
E=(1/T)*integral(f5,-T/2,0)+(1/T)*integral(f6,0,T/2);

Answer 1

[Jai Harnas]

Manages to do what i said and got rid of the error, the function now plots and the notation is a bit messy, but everything works.

%turning values n=1:10 to conjugates for i=-1:-10
cc=conj(c);

%series addition for k=-10:10
k=1:10
s=@(t) c0+(sum(c(k).*exp(1j*k*w*t))+(sum(cc(k).*exp(1j*-1*k*w*t))));

fplot(s,[-pi,pi])

However, i still get the Warning: Function behaves unexpectedly on array inputs. and any advice on how to fix this to make it work properly would be appreciated. Thank you

[Walter Roberson]

w=2; %angular frequency
T=(2*pi)/w; %working out the period

f1=@(t)(4+t)/2; %f(t)
f2=@(t) (2-t).*cos(2*t); %f(t)

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

for n = 1:10
    f3=@(t) ((4+t)/2).*exp(-1j*n*w*t);
    f4=@(t) ((2-t).*cos(2*t)).*exp(-1j*n*w*t);
    c(n,1)=(1/T)*integral(f3,-T/2,0)+(1/T)*integral(f4,0,T/2);
end 

cc=conj(c);

%c and cc and k must be column vectors for the below to work properly. t
%will be received as a row vector.

k = (1:10).';
s=@(t) c0 + sum(c(k).*exp(1j.*k.*w.*t),1) + sum(cc(k).*exp(1j.*-1.*k.*w.*t),1);


fplot(s,[-pi,pi])

[Jai Harnas]

That makes sense, Thank you!

Answer 2

[Walter Roberson]

s=@(t) symsum(c(k).*exp(1j*k*w*t),-10,10);

c is an array. k is symbolic variable . You can never use a symbolic variable as an index.

Make t symbolic and k=-10:10 and take a definite sum. Then use matlabFunction to convert into a numeric function.

You will then encounter the problem that you are trying to take c(-10) but c is a vector.

[Jai Harnas]

Thank you that makes a lot of sense. Is there anyway that i can overcome this problem? Maybe a way to convert the 10 values for c from a+jb to a-jb and do two different definite sums that way whilst leaving k=0 out, as it is calculated seperately?