---

function pushbutton2_Callback(hObject, eventdata, handles)

f_str = get(handles.edit1, 'String');
a = str2double(get(handles.edit2, 'String'));
b = str2double(get(handles.edit3, 'String'));

% делаем функцию векторной
f_str = strrep(f_str,'^','.^');
f_str = strrep(f_str,'*','.*');

f = @(x) eval(f_str);

result = integral(f, a, b);

set(handles.edit4, 'String', num2str(result));