Error of "Integrand output size does not match the input size."

Hello,

I am trying to make a double integral over two equtions, respectively. The equations are as following:

v_induced = u .* (1 + a_fit);
v_slipstream = u .* (1 + (2 .* a_fit));

bl_induced = @(u,z) Oper.rho .* (v_induced ./ Oper.Vinf) .* 0.5 .* (Oper.Vinf^2 - (v_induced .^2));
ke_out_induced = @(u,z) Oper.rho .* (v_slipstream ./ Oper.Vinf) .* 0.5 .* ((v_slipstream - Oper.Vinf).^2);

% Perform double integral
q1_induced = integral2(bl_induced, 0, delta99, 0, 2*pi);      
q2_induced = integral2(ke_out_induced, 0, delta99, 0, 2*pi);

D_induced = q1_induced + q2_induced;

However, when I am trying to make a double integral, MATLAB throws an error

Integrand output size does not match the input size.

u and a_fit is 1x30 double, and Oper.Vinf and Oper.rho are 1x1 double. I have checked the dimension but I don't see any problem.

Does anyone know what is wrong in my code?

I appriciate any help. Thanks.

Answer 1

[Yi-Kai Peng]

Turns out I didn't assign the correct input to the function...

It should be bl_induced = @(v_induced ,z) instead of bl_induced = @(u,z).

Thanks for all the help!

[Torsten]

What was z ?

And notice that your settings before

v_induced = u .* (1 + a_fit);

v_slipstream = u .* (1 + (2 .* a_fit));

are not used in the calculation of the two double integrals.

[Yi-Kai Peng]

Hello Torsten,

yes I noticed that those two variables are not used in the calculation. Do you know any way to solve this problem? Also, z is the second integral that I want to integrate in azimuthal direction (0 to 2*pi).

Answer 2

[Torsten]

As written,

Oper.rho .* (v_induced ./ Oper.Vinf) .* 0.5 .* (Oper.Vinf^2 - (v_induced .^2));

and

Oper.rho .* (v_slipstream ./ Oper.Vinf) .* 0.5 .* ((v_slipstream - Oper.Vinf).^2);

are constant arrays of size 1x30 that do not depend on the formal integration parameters u and z.

So in principle, you integrate a constant vector over the rectangle [0, delta99] x [0, 2*pi].

I guess this is not what you want.

The error message stems from the fact that MATLAB expects a vector of the size of u and z as output from your function handle. But you always return the constant array of size 1x30.