Not enough input errror

function [ x ] = cubicroots( a, b, c, d )

% find the real roots of the cubic equation ax^3 + bx^2 + cx + d

%   input parameters

%       a = real coefficient of cubic equation

%       b = real coefficient of cubic equation

%       c = real coefficient of cubic equation

%       d = real coefficient of cubic equation

%   output parameter

%       x = 1 x 3 vector containing the 3 roots of the cubic equation

D=18*a*b*c*d-4*b^3*d+b^2*c^2-4*a*c^3-27*a^2*d^2;

D0=b^2-3*a*c;

D1=2*b^3-9*a*b*c+27*a^2*d;

k=D1^2-4*D0^3;

u1=1;

u2=(-1+i*sqrt(3))/2;

u3=(-1-i*sqrt(3))/2;

C=((D1^2+sqrt(k))/2)^(1/3);

if D<0

      x(1)=(-1/3*a)*(b+u1*C+(D0/u1*C));

      x(2)=NaN;

      x(3)=NaN;

else

      x(1)=(-1/3*a)*(b+u1*C+(D0/u1*C));

      x(2)=(-1/3*a)*(b+u2*C+(D0/u2*C));

      x(3)=(-1/3*a)*(b+u3*C+(D0/u3*C));

end

error line 16 "not enough input arguments"

Answer 1

[Geoff Hayes]

laurae1234 - how are you calling this function? Given the signature,

   function [ x ] = cubicroots( a, b, c, d )

you need to provide four inputs. So calling this function as

 >> cubicroots

will generate the error

 Error using cubicroots (line xx)
 Not enough input arguments.

You need to pass in the coefficients of the cubic equation

 ax^3 + bx^2 + cx + d

If there is none, then pass in zero. For example, if the equation is

 x^3 + 2b^2 + 4

then you would call this function as

 >> cubicroots(1,2,0,4)

The above "works" in that it gives an answer, but I don't think it gives an accurate root of the cubic equation...