function dydt = expsin_deriv ( t, y )

%*****************************************************************************80
%
%% expsin_deriv returns the right hand side of the exponential sine test problem.
%
%  Licensing:
%
%    This code is distributed under the GNU LGPL license.
%
%  Modified:
%
%    17 September 2020
%
%  Author:
%
%    John Burkardt
%
%  Input:
%
%    real T, Y, the arguments of the derivative.
%
%  Output:
%
%    real DYDT, the value of the derivative.
%
  dydt = cos(t) .* y;

  return
end

