MATLAB: Error code : Error using optimoptions (line 105)

error codefminunc

when I enter the following command :
options = optimoptions('fminunc','Algorithm','trust-region','SpecifyObjectiveGradient',true);
Matlab displays the following error :
Error using optimoptions (line 105)
'SpecifyObjectiveGradient' is not an option for FMINUNC.
A list of options can be found on the FMINUNC documentation page.
I don't know this origin?
Thanks!