title: cannot open libmpfr.so.4 after update on ubuntu 18.04
body: <p>Today I updated my laptop to Ubuntu 18.04. 
  Now I try to run a program for my bachelor thesis, but it gives me the following error message: </p>
  
  <blockquote>
    <p>error while loading shared libraries: libmpfr.so.4: cannot open shared object file: No such file or directory</p>
  </blockquote>
  
  <p>I did a bit of research, and I think libmpfr4 has been droppen in this ubuntu version. Is there any way I can solve this? </p>