Subplot within for loop is duplicating/overlaying graphs.

The problem I am having is that the second plot seems to be overlaying the first one as well.

clear
syms x 
f(x)=1/cosh(x)

N=[4,14] %defines interpolating polynomial degree
for k=1:length(N) %iterates over the values in array N
    for i=0:N(k) %iterates over each point
        xcheb(i+1)=-0.5*cos((((2*i)+1)/(((2*N(k)))+2)*pi)); %creates array of Chebyshev points
        fvals(i+1)=1/cosh(xcheb(i+1)); %creates array of values of f(x) at each Chebyshev point
    end
    
    temp=1; %initialises temporary variable used in the Lagrange method
    poly(k)=0; %initialises poly; the integrating polynomial
    
    for i=1:N(k)+1
        for j=1:N(k)+1
            if i~=j
                temp=temp*(x-xcheb(j))/((xcheb(i)-xcheb(j)));
            end
        end
        poly=poly+(fvals(i)*temp);
        temp=1;
    end
    subplot(3,1,k)
    fplot(poly,[-0.5,0.5],'r')
end
subplot(3,1,3)
fplot(f,[-0.5,0.5],'g')

Thanks

Answer 1

[Walter Roberson]

poly(k)=0; %initialises poly; the integrating polynomial

That makes poly a vector . On the second iteration of k, poly is going to have length 2.

poly=poly+(fvals(i)*temp);

Vector plus scalar equals vector, so the left side is going to be a vector.

fplot(poly,[-0.5,0.5],'r')

All elements of the vector of symbolic experssions are plotted.

[Lewis]

Thank you, I forgot to include the 'k' index in the fplot line!