Input argument "xval" is undefined. Error in ==> vectorfield at 5 m=length(xval);

Hello, I am trying to run this program, but I've got this error message. Could you help me please to solve this problem? The script file is

 function vectorfield(deqns,xval,yval,zval)

t = 0;

      m=length(xval);
      n=length(yval);
      o=length(zval);

xxval = [];
yyval = [];
zzval = [];

x1=[];
y1=[];
z1=[];

for a=1:m
    for b=1:n
        for c = 1:o
            pts=feval(deqns,t,[xval(a);yval(b);zval(c)]);
            x1=[x1;pts(1)];
            y1=[y1;pts(2)];
            z1=[z1;pts(3)];

              xxval = [xxval; xval(a)];
              yyval = [yyval; yval(b)];
              zzval = [zzval; zval(c)];
          end
      end
  end

    arrow=sqrt(x1.^2+y1.^2+z1.^2);

u = x1./ar  if truerow;
v = x1./arrow;
w = x1./arrow;

quiver3(xxval,yyval,zzval,u,v,w);
axis tight;

Thanks

Answer 1

[Jan]

"xval" is undefined, if you did not provide it as input. You have to call this function in a way like:

vectorfield(@Equation, 1, 2, 3)

Due to the absence of a documentation in this function, I cannot guess how the inputs should look like exactly.

Please post a complete copy of the error message inside the text of the question. In this case, as in almost all others also, the complete message contains exactly the information I gave, but in a less specific formulation.