  We present modified Wang-Landau algorithm for models with continuous degrees
of freedom. We demonstrate this algorithm with the calculation of the joint
density of states $g(M,E)$ of ferromagnet Heisenberg models. The joint density
of states contains more information than the density of states of a single
variable--energy, but is also much more time-consuming to calculate. We discuss
the strategies to perform this calculation efficiently for models with several
thousand degrees of freedom, much larger than other continuous models studied
previously with the Wang-Landau algorithm.
