fractional-order differentiation problem

Hi friends

I am using a fractional-order differentiation function, dy=glfdiff(y,t,gam), for my project. but it does not answer correctly. I have tried it with a simple task as below:

t=0:.1:2*pi;
x=sin(t);
dx=glfdiff(x,t,1);
plot(t,x)
hold on
plot(t,dx,'r')

I think dx should has a cosine shape, but it doenst, can any one help me?

this is the glfdiff function:

https://www.mathworks.com/matlabcentral/mlc-downloads/downloads/submissions/60874/versions/1/previews/fractional/glfdiff.m/index.html