Quad error, simple function,
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I am a beginner, so please bear with me
cpn is referenced as such as this is part of a much larger code
clc
clear all
close all
cpn=[29105 8614.9 1701.6 103.47 909.79];
fun=@ (ll) cpn(1)+cpn(2)*((cpn(3)./ll)/sinh(cpn(3)./ll))^2+cpn(4)*((cpn(5)./ll)/cosh(cpn(5)./ll))^2
fun(100)
fun(200)
Q=quad(fun,18,200)
I am getting this error:
Error using quad (line 71) The integrand function must return an output vector of the same length as the input vector.
Error in Inttry (line 11) Q=quad(fun,18,200)
Thanks
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Réponses (2)
Roger Stafford
le 21 Août 2014
Your function definition is lacking operators in at least four places, one after "cpn(2)", one after "cpn(4)", and one before each of the two 2's. As such it does not constitute a valid matlab function definition.
4 commentaires
Roger Stafford
le 21 Août 2014
That looks like something that would work properly. Does it work, and is it the function you intended as the integrand?
Iain
le 21 Août 2014
I guess that you've missed off declaring a few operations as elementwise operations, and it's getting out a square matrix instead of a vector.
Each divide, multiply and power should have a "." just before them.
2 commentaires
Roger Stafford
le 21 Août 2014
The documentation of 'quad' at
http://www.mathworks.com/help/matlab/ref/quad.html
gives you the answer: "The function y = fun(x) should accept a vector argument x and return a vector result y, the integrand evaluated at each element of x."
This means that 'quad' doesn't send out just scalar quantities to be evaluated. It asks for entire vectors in x to be evaluated to the corresponding vectors y. That means that your expression which works for scalars but is inappropriate for vectors, will not succeed in 'quad'. You must put in those dots as Iain has recommended if you are to avoid the error messages and obtain a correct result.
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