# Integrating a function including mvnpdf. Error: Input function must return 'double' or 'single' values. Found 'sym'.

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Commented: ASKH on 30 Oct 2019
Hi,
I want to integrate the function fun below. It consists of a variable X multiplied by the multi-variable pdf of X and the correlated variable Y.
I get the error message "Input function must return 'double' or 'single' values. Found 'sym'." (see below).
fun = @(Y,X) X .* mvnpdf([X Y],mu,sigma); %where mu is 1-by-2 and sigma is 2-by-2
u = @(Y) log(C) + Y; %where C is a scalar constant
test = integral2(fun,-inf,inf,-inf,u);
Error using integral2Calc>integral2t/tensor (line 231)
Input function must return 'double' or 'single' values. Found 'sym'.
When I let X and Y be independent, so replace mvnpdf(....) by the product of their marginal pdfs, it works (then I redefine the variables and use lognpdf). I believe the error comes from the fact that my function fun gives symbolic output, even when supplied with arguments:
fun(1,2)
ans =
2*exp(- (5*conj(X) - conj(Y))^2/48 - conj(Y)^2/2 - 261924464376925987/144115188075855872)
But why is this? Is this the reason I cannot integrate my function? Grateful for help! Thanks!

Catalytic on 29 Oct 2019
Yes, that is the reason. Maybe you have made sigma or mu symbolic variables?
Hi,
Thanks for your response! No, sigma and mu are numbers (doubles):
mu =
0 0
sigma =
1.0000 0.2000
0.2000 1.0000
Do you have any idea for why my function would not give numbers as output? Perhaps I need to restrict the (X,Y) to be only real? Why are their complex conjugates showing up? Or does the mvnpdf not have a closed form...?

R2019a

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