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   Creates a set of first order differential equations to model
   a thermal circuit. Inputs are the nodal masses,
   a conductive node map, a radiative
   node map, an input node map and an output node map. The output
   is a set of first order differential equations in the form
   .
   T = aT + bq
   y = cT

   where T is the nodal temperature, q is the thermal input
   and y is the vector of measurements.

   A node map has one row for each node and as many columns as
   are necessary to specify the connections.
   Each node map is accompanied by a coefficient map that gives
   either the conductive or radiative heat transfer coefficents
   for the node pair. Radiative heat transfer is of the form:

            4     4
   q   = a(T   - T  )
    ij      i     j 

   Thermnet linearizes about the nominal temperature. The result
   is

            3       3
   q   = a(T  T  - T  T )
    ij      ni i    nj j

   where the n indicates a nominal temperature. The radiative heat
   transfer coefficient causes an asymmetry between nodes.

   Thermnet will automatically make the a matrix symmetric for 
   conduction. Thermnet will warn you if you entered a coefficient 
   twice and the two were different. You only have to specify the 
   connection in one direction.

   If you want a node to conduct or radiate to infinity just
   input "inf" as the node to which it is radiating or conducting.
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   Form:
   [a, b, c, ac, ar] = Thermnet( mn, cnm, cc, inm, onm, rnm, rc, tnom )
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   ------
   Inputs
   ------
   mn          (1,n)    Thermal mass of each node
   cnm         (n,:)    Conduction node map
   cc          (n,:)    Conduction coefficients
   inm         (m,:)    Input node map (nodes with inputs)
   onm         (p,1)    Output node map (nodes with outputs)
   rnm         (n,:)    Radiation node map
   rc          (n,:)    Radiation coefficients
   tnom        (1,n)    Nominal temperature for linearization

   -------
   Outputs
   -------
   a           (n,n)    Plant matrix
   b           (n,m)    Input matrix
   c           (p,n)    Output matrix
   ac          (n,n)    Conduction part of the plant matrix
   ar          (n,n)    Radiative (quartic) coefficient matrix

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