ThermalEquilibrium

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   This function computes the thermal equilibrium for a system
   with conductive and radiative heat exchange.
   
   lT^4 + kT = bq

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   Form:
   [t, err] = ThermalEquilibrium( d, q, t, nIts, epsilon )
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   Inputs
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   d           (:)   System matrices data structure
                     .k   linear term
                     .l   quadratic term
                     .b   input matrix
   q           (:)   Input fluxes
   t           (:)   Node temperatures
   nIts        (1,1) Number of iterations
   epsilon     (1,1) Error

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   Outputs
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   t           (:)   Node temperatures
   err         (:)   Node temperature error

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