*Problem Akashi-Kaikyo bridge! in figure*

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 ?

Answer 1

[Walter Roberson]

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 .

Answer 2

[bym]

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?