About homotopy perturbation method for solving heat-like and wave-like   equations with variable coefficients
  We analyze a recent application of homotopy perturbation method to some heat-like and wave-like models and show that its main results are merely the Taylor expansions of exponential and hyperbolic functions. Besides, the authors require more boundary conditions than those already necessary for the solution of the problem by means of power series. 
Francisco M. Fernandez