Error using the function procest

   Hi,

   I don't can use procest function ?

   I've been using arx function (data, sys, ts), oe (data, sys, ts) and have no problem in obtaining the results, then use compare (sys, sys1, SYS2).

   The problem I have to use procest(data, type). I use this code:

Ts = 1;

ze = iddata(output1,input1,Ts,'TimeUnit','seg');

type = idproc('P1D');

result=procest(ze,type);

   Getting error:

??? Undefined function or method 'procest' for input arguments of type 'idproc'.

Error in ==> prueba_process_model at 30 result=procest(ze,type);

    I use the version R2011a is possible that this version may not work with this function even appear in the help of this release??.

   Thanks for your time.