# Error using quad "Error using quad (line 75) The integrand function must return an output vector of the same length as the input vector."

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jayash on 25 Feb 2015
Commented: Star Strider on 25 Feb 2015
I have edited the code according to answers.
Can anyone explain the reason behind the errors and help me correcting the following code:
U = 1;
e = @(q) 2*(1-cos(2*pi*q));
hq = @(q,n0) ((e(q)).^2+2*U*n0*(e(q))).^0.5;
y = @(q,n0) (((e(q))+(U*n0))/hq(q,n0))-1;
a = -0.5;
b = 0.5;
cv =@(n0) n0+(0.5*v(n0))-1;
while U < 20
n0 = 0.1;
options = optimset('Display', 'iter');
n = fsolve(cv(n0),n0,0.1,options);
plot(U,n)
hold on
U = U + 1;
end
Errors:
The integrand function must return an output vector of the same length as the input vector.
Error in @(n0)n0+(0.5*v(n0))-1
Error in simulv1 (line 12)
n = fsolve(cv(n0),n0,0.1,options);

Star Strider on 25 Feb 2015
You forgot to fully vectorise those equations. Change them to:
hq = @(q,n0) ((eq(q)).^2+2*U*n0*(eq(q))).^0.5;
y = @(q,n0) (((eq(q))+(U*n0))./hq(q,n0))-1;
and see if that helps.
Star Strider on 25 Feb 2015
@jayash — Evaluate ‘y(q,n0)’ (and your other functions as well) for representative values of both arguments to see what it does. Always evaluate the functions you give to solver routines first to be certain that they work and give you the results you expect.
@A Jenkins — Thank you. That very well could be the problem.

dpb on 25 Feb 2015
_"I am using .^ but..."
But you aren't, everywhere. The line given by the error message is--
hq = @(q,n0) ((eq(q))^2+2*U*n0*(eq(q))).^0.5;
The term (eq(q))^2 doesn't have a 'dot' operator just as the error says.
BTW, do NOT use eq as a variable or function name; that aliases the builtin logical "equal" function == or eq()
>> which eq
built-in (C:\ML_R2012b\toolbox\matlab\ops\@double\eq) % double method
>>
jayash on 25 Feb 2015
thanks for your suggestion on "eq", I corrected accordingly.

A Jenkins on 25 Feb 2015
There are two powers in that line and you have only replaced one.
@(q,n0)((eq(q)) ^ 2+2*U*n0*(eq(q))) .^ 0.5

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