Here are the ways to covary pairs and specify sets:
```
% Vary two parameters (run a simulation for all combinations of values)
% vary={'E','(EK,ENa)',[-80 -60]}; % checked
% This sets modifications:
% * E_EK, E_ENa = -80
% * E_EK, E_ENa = -60
% vary={'E','(EK,ENa)',[-80 -60; -85 -65]}; % checked
% This sets modifications:
% * E_EK = -80 and E_ENa = -85
% * E_EK = -60 and E_ENa = -65
% vary={'E','(EK,ENa,Iapp)',[-80 -60; -85 -65; 0 1]}; % checked
% This sets modifications:
% * E_EK = -80, E_ENa = -85, Iapp = 0
% * E_EK = -60, E_ENa = -65, Iapp = 1
% vary={'E','(EK,ENa,Iapp)',[-80 -50 -60; -85 -40 -65; 0 2 1]}; % checked
% This sets modifications:
% * E_EK = -80, E_ENa = -85, Iapp = 0
% * E_EK = -50, E_ENa = -40, Iapp = 2
% * E_EK = -60, E_ENa = -65, Iapp = 1
%
% vary={'(E,I)','(EK,ENa)',[-80 -60]}; % checked
% This sets modifications:
% * E_EK, E_ENa, I_EK, I_ENa = -80
% * E_EK, E_ENa, I_EK, I_ENa = -60
% vary={'(E,I)','(EK,ENa)',[-80 -60; -85 -65]}; % checked
% This sets modifications:
% * E_EK, I_EK = -80 and E_ENa, I_ENa = -85
% * E_EK, I_EK = -60 and E_ENa, I_ENa = -65
% vary={'(E,I)','(EK,ENa)',cat(3,[-80 -60], [-85 -65])}; % checked
% This sets modifications:
% * E_EK, E_ENa = -80 and I_EK, I_ENa = -85
% * E_EK, E_ENa = -60 and I_EK, I_ENa = -65
% vary={'(E,I)','(EK,ENa)',cat(3, [-75 -55; -80 -60], [-85 -65; -90 -70])}; % checked
% This sets modifications:
% * E_EK = -75, E_ENa = -80, I_EK = -85, I_ENa = -90.
% * E_EK = -55, E_ENa = -60, I_EK = -65, I_ENa = -70.
```