Lagrange Polynomial not plotting in Octave

Question

The question requires a Lagrange polynomial L(c) to replace the complicated-looking function, f. Also, plot function f and L(c) between [1:0; 10:0]. However, after the code computes the values for k, it cannot seem to create a plot and a graph. What am I doing wrong? Attached is the code below. Thank You!

clear
pkg load symbolic
graphics_toolkit('gnuplot')
syms m x
c = []
for i = 1: 0.5 : 10
  c = [c,i]
endfor
d = length(c)
k = []
f = 3.* (1 .- ( 8 ./ vpa(pi.^2) .* ((1 ./ cosh(vpa(pi) .* vpa(x) ./ 2)) .+ symsum(1 ./ ((2 .* m .+ 1).^2 .* cosh((2 .* m .+ 1) .* vpa(pi) .* vpa(x) ./ 2)), m,1 ,Inf)))) ./ ((1 .- ( 192 ./ vpa(x) .* vpa(pi.^5)).*(tanh(vpa(pi) .* vpa(x) ./ 2) .+ symsum(tanh((2 .* m .+ 1) .* vpa(pi) .* vpa(x) ./ 2) ./ (2 .* m .+ 1).^5, m,1 ,Inf))));
for i = 1:d
  A = (1 - ( 192 / vpa(c(i)) * vpa(pi^5))*(tanh(vpa(pi) * vpa(c(i)) / 2) + symsum(tanh((2 * m + 1) * vpa(pi) * vpa(c(i)) / 2) / (2 * m + 1)^5, m, 1, Inf)))
  B = 1 - ( 8 / vpa(pi^2) * ((1 / cosh(vpa(pi) * vpa(c(i)) / 2)) + symsum(1 / ((2 * m + 1)^2 * cosh((2 * m + 1) * vpa(pi) * vpa(c(i)) / 2)), m, 1, Inf))) 
  K = 3 * B / A
  k = [k,K]
endfor
col = c(1)
matrixc = [];
for m = 1:d;
  prod = 1;    
  for t = 1:d
    if col == ((m+1)/2)
      col = col .+ ((10-1)/(d-1));
    endif   
    sol = (x.-vpa(col))./(vpa((m+1)/2).-vpa(col));
    prod = prod*sol;   
    col = col .+ ((c(2)-c(1))/(d-1));  
  endfor
  h = k(m);
  p = vpa(h).*prod;
  matrixc = [matrixc,p];
  col = 1;
endfor
L=sum(matrixc);
L
ezplot(L,[c(1),c(d)]);
hold on;
k(1)
plot(c,k);
legend('Lagrange Polynomial','K(x)');
xlabel('x-axis');
ylabel('y-axis');```

Answer 1

You are trying to plot a symbolic variable. I don't know if this is possible in general, but in this particular case at least the conversion is causing problems

Collect the values of the symbolic variable first, by casting to double , and then you can plot as intended:

plot( c, double(k) );