Riemanns_integral error

I am trying to use rsums for riemanns. For this equation . I know it simplifies down too umax=2uavg but its more for evidence using the 2 methods mentioned before. my main problem for Riemanns is having this error. could someone explain what I am doing wrong?

Error using sym/rsums

Too many output arguments.

Error in LiveEditorEvaluationHelperESectionEval>Riemanns_integral (line 122)

B1 = rsums(B,[0,R],r);

Error while evaluating UIControl Callback

function Riemanns_integral(~,~) % value entery for the function
uavg = input('average velocity m/s   ');
R= input('inner radius m   ');
syms r
T = uavg*pi*R^2;
B = (1-(r/R)^2)*r;
B1 = rsums(B,[0,R],r);
B2 = rsums(B1,[0,2*pi],x)
UmaxRI = T/B2

Answer 1

[KALYAN ACHARJYA]

Error using sym/rsums
Too many output arguments.

If you check the MATLAB docs of rsums: Which is function for displays a iteractive graph

"rsums(f) displays a iteractive graph of f(x) using 10 terms (rectangles).", Hence it might be not accept any output arguments (probable reason).

function Riemanns_integral(~,~) % value entery for the function
uavg = input('average velocity m/s   ');
R= input('inner radius m   ');
syms r
T = uavg*pi*R^2;
B = (1-(r/R)^2)*r;
rsums(B,[0,R]);
%B2 = rsums(B1,[0,2*pi],x)
%UmaxRI = T/B2

[Coolman]

strange my lecturer told me that I have to use Riemanns integral to get the answer of the double intergral any idea how I could do it then?