2 MODIFY
  Syntax: MODIFY K UK WK AK BK
   where: K   is the MINUIT parameter number you want to modify.
          UK  is its value.
          WK  is its starting error.
          AK  is its lower limit (if any).
          BK  is its upper limit (if any).

  Modify, fixes  and/or   restores  MINUIT  parameters.  In  addition, a
  parameter with(out)  limits can be changed to  have not (have) limits.
!\index{limits}
  Each of last 4 parameters can be specified as a (floating) number or a
  register, parameter etc. or as the  character `=' which means keep the
  present value.

  `MODIFY' will reset `ISW(2)' to zero, meaning that all fits start from
  rock bottom (i.e. `SIMPLEX'). The covariance matrix is also killed.

  In the CERN version `MODIFY' completely redefines the
  parameter. Thus if you set the error to 0, the parameter is constant
  and can only be made variable again by using the `MODIFY' command -
  `FLOAT' does not work.

  In the C.  Rippich  version a  parameter that  was fixed  in the input
  dialogue stays fixed for all eternity!

