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
jayash 2015-2-25
评论： Star Strider 2015-2-25
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);

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采纳的回答

Star Strider
Star Strider 2015-2-25
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.
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显示 3更早的评论
A Jenkins
A Jenkins 2015-2-25
I would guess that your y is the wrong size because you have missed Star Strider's second suggestion: that you also need ./ instead of / in the line that calculates y.
Star Strider
Star Strider 2015-2-25
@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.

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更多回答（2 个）

dpb
dpb 2015-2-25
_"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 2015-2-25
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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