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

16 views (last 30 days)
jayash
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;
v = @(n0) quad(@(q) y(q,n0),a,b);
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:
Error using quad (line 75)
The integrand function must return an output vector of the same length as the input vector.
Error in @(n0)quad(@(q)y(q,n0),a,b)
Error in @(n0)n0+(0.5*v(n0))-1
Error in simulv1 (line 12)
n = fsolve(cv(n0),n0,0.1,options);

Accepted Answer

Star Strider
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.
  5 Comments
Star Strider
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.

Sign in to comment.

More Answers (2)

dpb
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
>>

A Jenkins
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

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by