Hi,
you have two options: either, the popupmenu1_Callback stores the values for I, V, p using e.g. guidata and the pushbutton1_Callback retrieves them. Add at the end of popupmenu_Callback:
handles.data.I = I;
handles.data.V = V;
handles.data.p = p;
guidata(hObject, handles);
and in the pushbutton1_Callback use them:
I = handles.data.I;
Alternative: move the code you've written in popupmenu1_Callback to pushbutton1_Callback, i.e., when you click the pushbutton, the value from the popupmenu is read and the values computed.
Titus
