Mass-spring-damper models

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File:Mkdsys.m

Gives a MIMO mass-spring damper system for force input and position output
the number of masses is determined from the given array
of masses!

Usage:   struct=mkdsys(m,k,d);

Inputs:  m is an nx1 array containing the n masses      [m1 m2 m3]
         k is an n+1x1 array containing the n+1 springs [k1 k2 k3 k4]
         d is an n+1x1 array containing the n+1 dampers [d1 d2 d3 d4]
          
         example for n=3:
                     ____        ____        ____                                                         
          ///|  k1  |    |  k2  |    |  k3  |    | k4   |///                                                                                                                             
          ///|/\/\/\| m1 |/\/\/\| m2 |/\/\/\| m3 |/\/\/\|///                                                           
          ///|  d1  |____|  d2  |____|  d3  |____| d4   |///                                                     
                                                                              

Outputs:  sys.ss : state-space system also sys.A,sys.B,sys.C,sys.D
          sys.M  : mass matrix 
                    sys.K  : stiffness matrix
          sys.D  : damping matrix
          and some more modal things in the struct
         

Author

Rob Hoogendijk