function setEnergy(r, flag)
% SETENERGY  Enable or disable solving the energy equation.
% setEnergy(r, flag)
% If the energy equation is disabled, then the reactor temperature is
% constant. The parameter should be the string ``'on'`` to enable the
% energy equation, or ``'off'`` to disable it.
%
% By default, Reactor objects are created with the energy equation
% enabled, so usually this method is only needed to disable the
% energy equation for isothermal simulations. ::
%
%     >> setEnergy(r, 'on');
%     >> setEnergy(r, 'off');
%
% :param r:
%     Instance of class :mat:func:`Reactor`
% :param flag:
%     String, either ``'on'`` or ``'off'`` to enable and disable
%     solving the energy equation, respectively
%

iflag = -1;
if strcmp(flag, {'on'})
    iflag = 1;
elseif strcmp(flag, {'off'})
    iflag = 0;
end
if iflag >= 0
    reactormethods(9, r.index, iflag)
else
    error('Input to setEnergy not understood.');
end