differentiating a function and filling in values from excel

hello

Below I wanted to do the following. Calculate the first derivative and second derivative of a function. Next fill in the values of a,b,c and d with values from an excel table for each row.

My problem is that I can generate the f,df and d2f function using the diff formula. Also I can fill in the values for a,b,c and d using the subs formula for f. This doesn't seem to work for df and d2f. If i use subs the returning formulas for f and d2f are the same: f as many times there are rows in excel for each row in f. (in my case 10 times 10)

How can I use .*,.^,./ operators on df and d2f?

% analytical deriving f, df and d2f

t=sym('t');
a=sym('a');
b=sym('b');
c=sym('c');
d=sym('d');
f=a.*t.^3+b.*t.^2+c.*t+d
df=diff(f,t,1)
d2f=diff(f,t,2)

% import excelfile to replace variables

ar=xlsread('test0','A:A');
br=xlsread('test0','B:B');
cr=xlsread('test0','C:C');
dr=xlsread('test0','D:D');

f=subs(f,{a,b,c,d},{ar,br,cr,dr})
df=subs(f,{a,b,c,d},{ar,br,cr,dr})
d2f=subs(f,{a,b,c,d},{ar,br,cr,dr})

% obtain the AH,T1,T2,V1,V2,H1,H2