powMrec

Power of M matrix by recurrence.


Syntax
   F = powMrec(x, order)

Description
   F = powMrec(x, order) is a faster and stable way to compute M^order, 
   order = 2, 3, ... Was avoided the direct products of these matrices, 
   and instead that we applied a reccurrence formulation: 
           m_{i, j}^(order) = m_{i-1, j}^(order-1)*alpha_{i-1} +
                             m_{i, j}^(order-1)*beta_{i} +
                             m_{i+1, j}^(order-1)*gamma_{i+1}, 
   where alpha, beta and gamma are the coefficients of orthogonal 
   polynomials three term recurrence relation, shifted to [a, b].

Inputs
   x     = independent tau variable (itau object).
   order = power order (integer).

Output
   F     = x^order = M^order (double matrix).