heateqn_nb.solve_tridiagonal
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.. py:function:: heateqn_nb.solve_tridiagonal(a, b, c, d)

   a: sub-diagonal (len n-1), A[i, i-1]
   b: main diagonal (len n), A[i, i]
   c: super-diagonal (len n-1), A[i, i+1]
   d: RHS (len n)