# Having difficulty performing symbolic integral

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Faraz Vossoughian on 18 Dec 2017
Answered: Walter Roberson on 20 Dec 2017
In my code the part im trying to calculate A0 , A1,A2 and zerolift i get the following error
Error using sym/subsindex (line 836)
Invalid indexing or function definition. Indexing must follow
MATLAB indexing. Function arguments must be symbolic variables,
and function body must be sym expression.
Error in sym/subsref (line 881)
R_tilde = builtin('subsref',L_tilde,Idx);
Error in TEST2 (line 10)
A=int(dzdx,tetan,0,pi);"
Thank you,
my code is below
zc= 0.48*xc*(xc-1)^2;%change
dzdx=diff(zc,xc);%change
xc=0.5*(1-cos(tetan));
dzdx=(12*xc*(2*xc - 2))/25 + (12*(xc - 1)^2)/25;
%A0
A=int(dzdx,tetan,0,pi);
int=A/pi;
Anot=alpha-(A)
%A1
n=1
B=int(dzdx*(cos(1*tetan)),tetan,0,pi);%first part
A1=(2/pi)*(B)
%A2
n=2
C=int(dzdx*(cos(2*tetan)),tetan,0,pi);%first part
A2=(2/pi)*(C)
%zerolift
D=int((cos(tetan)-1)*dzdx,tetan,0,pi)
alphaZ=(-1/pi)*D;

Amy on 20 Dec 2017
Faraz, I think you are running into this issue because of the following line:
int = A/pi;
Then you run into an error the next time you try calling the int function because it is " shadowed". Try renaming that variable something else and you should no longer run into the same error.

Walter Roberson on 20 Dec 2017
As I said then, do not use int as a variable name. I suggested replacement code there.