function [out] = ChemReac(x, y, flag)%%  Evaluate the right hand side function for the%  chemical reaction system%%    y_1'(x) = -k1*y_1(x) %    y_2'(x) =  k1*y_1(x) - k2*y_2(x)%    y_3'(x) =              k2*y_2(x)%%%global k1 k2switch( flag )   case '' % return right hand side      out  = [ -k1   0   0;                k1  -k2  0;                0    k2  0 ]* y;      case 'jacobian' % return Jaacobian of right hand side      out  = [ -k1   0   0;                k1  -k2  0;                0    k2  0 ];      otherwise      error(['Unknown request .'])end