# Error using integral2

5 views (last 30 days)
Shahid Hasnain on 15 Nov 2018
Commented: Star Strider on 3 Dec 2018
I have following expression with
x=[1 2 3 4 5]
y=[1 2 3 4 5]
L = 100; % Length of the box
p=1;
q=1;
Ui = @(x,y) sin(pi*x).*sin(pi*y); % An initial distribution for u, i.e. the u(x,y,0)
Vi = @(x,y) sin(pi*x).*sin(pi*y); % An initial distribution for v, i.e. the v(x,y,0)
Wi = Ui(x,y) + Vi(x,y); % Initial condition for w, i.e. w(x,y,0)
% Computation of the b-coefficients
if p < Ntrunc
if q < Ntrunc
my_integrand = @(x,y) 4*Wi.*sin(p.*x).*cos(q.*y)/L^2;
bd(p,q) = integral2(my_integrand(x,y),0,L,0,L);
q = q+1;
end
p = p+1;
end
I got following error,
Error using integral2Calc>integral2t/tensor (line 231)
Input function must return 'double' or 'single' values. Found 'function_handle'.
Error in integral2Calc>integral2t (line 55)
[Qsub,esub] = tensor(thetaL,thetaR,phiB,phiT);
Error in integral2Calc (line 9)
[q,errbnd] = integral2t(fun,xmin,xmax,ymin,ymax,optionstruct);
Error in integral2 (line 106)
Q = integral2Calc(fun,xmin,xmax,yminfun,ymaxfun,opstruct);
Correction will be highly appreciated.
madhan ravi on 15 Nov 2018

Star Strider on 15 Nov 2018
Edited: Star Strider on 15 Nov 2018
This works, although it throws a warning:
Ntrunc = 100;
L = 100; % Length of the box
p=1;
q=1;
Ui = @(x,y) sin(pi*x).*sin(pi*y); % An initial distribution for u, i.e. the u(x,y,0)
Vi = @(x,y) sin(pi*x).*sin(pi*y); % An initial distribution for v, i.e. the v(x,y,0)
Wi = @(x,y) Ui(x,y) + Vi(x,y); % Initial condition for w, i.e. w(x,y,0)
% Computation of the b-coefficients
if p < Ntrunc
if q < Ntrunc
my_integrand = @(x,y) 4*Wi(x,y).*sin(p.*x).*cos(q.*y)/L^2;
bd(p,q) = integral2(@(x,y)my_integrand(x,y),0,L,0,L);
q = q+1;
end
p = p+1;
end
I defer to you to correct the problem that produces the warning.
EDIT — Corrected typographical error.
Star Strider on 3 Dec 2018
Do you want to integrate a system of partial differential equations? If so, please post this as a new Question. My experience with the Partial Diufferential Equation Toolbox is limited, although Torsten and some others here likely have significant experience with it. I have not worked with it in a while, so it would take some time for me to provide you with a response.

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