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## Numerical integration with quadcc

**From**: |
BGreen |

**Subject**: |
Numerical integration with quadcc |

**Date**: |
Fri, 7 Jun 2019 14:25:07 -0500 (CDT) |

My problem is that I get the error "integrand F must return a single,
real-valued vector of the same size as the input" even when the integrand
DOES return such a vector. I am using quadcc because I have infinite limits
of integration and a piecewise-defined integrand. Things will execute
correctly if I just use quad, but I'm not sure whether or not the answer
will be trustworthy since the documentation recommends other integrators for
infinite bounds and nonsmooth functions.
I call the following within a function:
Vsame = @(x) Vsame_fit(x./lB);
F0011 = @(x) (1-(x.^2)/2).*exp(-(x.^2./2));
integ_F0011same = @(x) F0011(x).*Vsame(x);
integ_F0011same(linspace(1,3,10))
Fsame(1,1,2,2) = quadcc(integ_F0011same,0,Inf);
I defined the constant lB elsewhere. Outside that function I have defined
Vsame_fit:
function y = Vsame_fit(q)
for k=1:length(q)
if q(k)<0.022913
y(k) = 0.98*tanh(200*q(k));
elseif q(k)<0.50274
y(k) = 1/(0.9*q(k)+1);
elseif q(k)<21.598
y(k) = 1/(1.046*q(k)+0.9266);
else
y(k) = 1/(0.9512*q(k)+2.89);
end
end
end
I wrote the loop over the length of the argument to ensure that it would
return a vector. Furthermore, if I call something simple as a test like
integ_F0011same(linspace(1,3,10))
inside the function, a 10-element is returned as expected. Why am I getting
this error?
At the end of the day, I just want to have the value of the integral which I
was hoping would be saved to Fsame(1,1,2,2). The reason I have defined
things with so many separate functions, however, is that I reuse Vsame three
more times to evaluate similar integrals, e.g.
integ_F0110same = @(x) F0110(x).*Vsame(x);
Fsame(1,2,2,1) = quadcc(integ_F0110same,0,Inf);
where F011(x) was also defined with a function handle. Is there a better way
I should be doing this?
--
Sent from: http://octave.1599824.n4.nabble.com/Octave-General-f1599825.html

**Numerical integration with quadcc**,
*BGreen* **<=**