Why can't I solve this ODE set?

I tried to use Mathematica to solve this OED set:
DSolve[{y''[r] + (1/r + 2 I p) y'[r] + (-2 h + 2/r - m^2/r^2 - p^2) y[r] == 
 2 a z[r], 
z''[r] + (1/r - 2 I p) z'[r] + (-2 h + 2/r - m^2/r^2 - p^2) z[r] == 
 2 a y[r]},{y,z}r] .
But as I input it, nothing works. Mathematica just give back the same equations to me. Interestingly, either of the 2 equations can be solved separately, including the other in its expression. I mean:
DSolve[y''[r] + (1/r + 2 I p) y'[r] + (-2 h + 2/r - m^2/r^2 - p^2) y[
     r] == 2 a z[r], y[r], r]
DSolve[z''[r] + (1/r - 2 I p) z'[r] + (-2 h + 2/r - m^2/r^2 - p^2) z[
      r] == 2 a y[r], z[r], r] /. y[r] -> % .
Would anybody please help me, or explain why this phenomenon occurs?

5/19/2014 6:04:56 AM
comp.soft-sys.math.mathematica 28821 articles. 0 followers. Follow

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