*Problem Akashi-Kaikyo bridge! in figure*

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justin Taylor
justin Taylor 2011-12-10
Figure http://i1203.photobucket.com/albums/bb396/kidstar079/sadas.png\
http://i1203.photobucket.com/albums/bb396/kidstar079/Capture.png mycode:
% Code find main cable bridge Akashi-Kaikyo
syms x;
% use line interals type I.
I=eval(int(sqrt(1+(diff(2*10^(-4)*x^2-0.4*x+200,x)^2)),0,1991))
--> Lenght cable= inf it rong ?

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采纳的回答

Walter Roberson
Walter Roberson 2011-12-10
You should not use eval() in that context: you should use double() instead.
I cannot say what MuPAD returns for that integral; Maple returns 2042.433965 .

更多回答（1 个）

bym
bym 2011-12-11
OK this is strange: if I do
a= int(sqrt(1+(diff(2*10^(-4)*x^2-0.4*x+200,x)^2)))
a =
1250*asinh(x/2500 - 2/5) + (x/2 - 500)*((x/2500 - 2/5)^2 + 1)^(1/2)
subs(a,1991)-subs(a,0)
ans =
2042.4
but if I do
a= int(sqrt(1+(diff(2*10^(-4)*x^2-0.4*x+200,x)^2)),0,1991)
matlab just hangs and doesn't respond; perhaps something with the definite limits?

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