Using eval undefined function or variable

So I have a exercise to solve a differential equation and I have to use Pikar's method to draw some of the approximations.However I have trouble using eval. Here is my code:

function ex1
hold on;
grid on;

xmin=1;xmax=3;
x0=2;y0=2;
axis([xmin xmax -1,5]);

y=dsolve('Dy=x*(3*y-2)*sin(1-4*x^2)','y(2)=2','x')

t=xmin:(xmax-xmin)/100:xmax;
plot(t,eval(y),'k');

function z = ff(x,y)
z=x.*(3*y-2).*sin(1-4*(x.^2));
end
% Calculating the approximations
X=xmin:(xmax-xmin)/100:xmax;
Y=y0*ones(1,length(X));
plot(X,Y,'y');
Z=Y;
N=8;
for k=1:N
    YK=y0+cumtrapz(X,ff(X,Z));

      if(k==1)
           plot(X,Y,'g');
      elseif(k==2)
          plot(X,Z,'b');
      elseif(k==7)
          plot(X,Z,'r');
      end
      Z=YK;
  end
  end

And the errors I am getting are :

Error using evalin
Undefined function or variable 'x'.

Error in sym/eval (line 11)
s = evalin('caller',vectorize(map2mat(char(x))));

Error in ex1 (line 12)
plot(t,eval(y),'k');

Answer 1

[Walter Roberson]

Do not eval() a symbolic expression. Symbolic expressions are in a language that is not MATLAB and is not MUPAD.

The result of the dsolve is the symbolic expression

(4*exp(-(3*cos(15))/8)*exp((3*cos(4*x^2 - 1))/8))/3 + 2/3

When you try to eval() that, you need to have a variable named x defined, but you do not.

sol = double( subs(y, sym('x'), t) );
plot(t, sol)