Why quad function can't communicate with my subfunction?

Hello, i have written two matlab functions to calculate the integral of functions which have a particular limit near zero.

first function:

function sinx

% This is the funtion file sinx.m
% Matlab functions quad and int are also used. The results are compared.

a=0; b=1; n=10;

S = simpson(@integrand, a, b, n);

Q = quad(@(x)integrand(x), a, b);

syms x;

E = double(int(sin(x)/x, x, a, b));

fprintf(' Simpson = %g\n Quad = %g\n Symbolic = %g\n ', S, Q, double(E))

function f = integrand(x)

if x>0

      f=sin(x)./x;

else                % If x-->0, f=1.
    f=1;
end

second function:

function bessel

% This is the funtion file bessel.m

L=1; n=10;

nx=20; x=linspace(0,L,nx+1);

Q = zeros(nx+1,1);

for i=1:nx+1

      a=x(1); xx=x(i); b=1-xx;
      S(i) = simpson(@integrand, a,b,n,xx);
      Q(i) = quad(@(t)integrand(t,xx), a ,b);

end

plot(x,Q,'k',x,S,'r');
legend('Quad','Simpson',0);
fprintf('e=%g\n', max(abs(Q-S))/max(abs(Q))*100)

function f=integrand(t,x)

z=sqrt((1-t).^2-x.^2);

if z>0

      f=sin(t).*besselj(1,z).*x./z;

else

      f=sin(t).*x/2;                      % besselj(1,z)/z -> .5 as z-> 0

end

Why in the first function (sinx.m) quad can't communicate with if/else, and matlab give me the error:

Error using quad (line 79) The integrand function must return an output vector of the same length as the input vector.

Thank you in advance for your help.

Answer 1

[Matt Fig]

If that is the error message, communication is not the problem. Re-read the message.... there is a problem with what your function returns.

Use this instead:

function f = integrand(x)
f = ones(size(x));
idx = x>0;
f(idx) = sin(x(idx))./x(idx);