How do I fix "Error using ==> mupadmex Error in MuPAD command: DOUBLE cannot convert the input expression into a double array. If the input expression contains a symbolic variable, use the VPA function instead." ?

This is my script and the error I get after I enter the series equation and starting k:

syms k 
series_eq = input('Enter equation(k = index): ');
a = input('Enter starting k (integer >= 1): ');
disp(' ')
p = limit(series_eq(k),k,inf,'left')
p = double(p);
fseries_eq = matlabFunction(series_eq);
k = a:(a + 999);
if abs(fseries_eq(k)) >= abs(fseries_eq(k + 1))
    if p == 0
        disp('The series equation:')
        series_eq
        disp('Is convergent.')
        disp(' ')
    else
        disp('The series equation:')
        series_eq
        disp('Is divergent.')
        disp(' ')
    end
else
    if p == 0
        disp('The series equation:')
        series_eq
        disp('May converge or diverge.')
        disp(' ')
    else
        disp('The series equation:')
        series_eq
        disp('Is divergent.')
    end
end
??? Error using ==> mupadmex
Error in MuPAD command: DOUBLE cannot convert the input expression into a
double array.

If the input expression contains a symbolic variable, use the VPA function instead.

Error in ==> sym.sym>sym.double at 936 Xstr = mupadmex('symobj::double', S.s, 0);

Error in ==> sym.sym>privformatscalar at 2678 x = double(x);

Error in ==> sym.sym>privformat at 2663 s = privformatscalar(x);

Error in ==> sym.sym>sym.subsref at 1379 [inds{k},refs{k}] = privformat(inds{k});

Error in ==> altlimit at 5 p = limit(series_eq(k),k,inf,'left')

Answer 1

[David Cazenave]

It's because your trying to convert a symbolic variable into a double precision number.