anchor.diff:          size_t m, int b, size_t kpast, size_t kfuture, double *pi,
           inform_error *err);
   ----
  +[horizontal]
  +Header:: `inform/predictive_info.h`
   ****
   
   [[relative-entropy]]
  
positive.code: // no need to free since `ai` was statically allocated in this scope
  // free(ai);
  ----
  ****
  
  [[block-entropy]]
  
negative.code:     double pi;
  } inform_pid_source;
  ----
  [horizontal]
  Header:: `inform/pid.h`
  ****
  
  ****
  