How can be the variable of one slider be independent on variable of another slider , initially ?

Hello all, I am using two sliders for generating cylinder (for altering R and H).code is -

 function slider1_Callback(hObject, eventdata, handles)
global a; global b;
a=get(hObject,'Value');
[xc,yc,zc] = cylinder(a);
zc(2,:)=b;
axes(handles.cylinder);
axis equal;
surf(zc,xc,yc,'Facecolor',[1 1 1]);

 function slider2_Callback(hObject, eventdata, handles)
global b; global a;
b=get(hObject,'Value');
[xc,yc,zc] = cylinder(a);
zc(2,:)=b;
axes(handles.cylinder);
axis equal;
surf(zc,xc,yc,'Facecolor',[1 1 1]);

when I slide first slider it gives error because initially second slider does not have any value ('b' is undefined). So when I change value of 2nd slider then 1st slider then it generates cylinder . How could I make 1st slider independent of b initially ? means when I slide first slider in the beginning it should response , should not give the error. Thank you .

Answer 1

[Walter Roberson]

Before

zc(2,:)=b;

add

if isempty(b)
  b = get(handles.slider2, 'Value');
end

[yogesh jain]

Thank you Mr. Roberson.