Problem with function handle? or something.

Question

Dakota Burrow 2013-7-7

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/81311-problem-with-function-handle-or-something

So, first off, the answer to this problem should be roughly .0028. But, somewhere in the code there is an issue and it will not compute correctly. Can you help?

clc
clear
v = input('Enter initial guess for the volume of methane: '); 
R = .518;
pc = 4600; 
tc = 191; 
T = -40 + 273; 
P = 65000; 
a = .427*R^2*tc^2.5/pc; 
b = .0866*R*tc/pc; 
gv =@(v)(R*T)-(((a*(v-b)^2)/(v*(v+b)*sqrt(T))) + P * b)/P;
n = 4;
es = .5*10^(2-n);
[r, I] = Redlich_Kwong(es, v, gv); 
fprintf('\nThe calculated volume is : %.6f',r); 
fprintf('\nIt took %1.0d iterations to converge.',I);

Function

function [r, I] = Redlich_Kwong(es, v, gv)
I = 0; 
ea = 1;
while ea > es
    r = gv(v); 
    ea = 100*abs((r-v)/r); 
    v = r; 
    I = I +1; 
end 
end

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Answer 1

Guru 2013-7-7

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/81311-problem-with-function-handle-or-something#answer_91032

Well, from plotting your input-output behavior of your anonymous function gv(), it converges to about the value of R*T. In other words, for all values of v, gv returns an answer of approximately R*T, so I would guess something is wrong in your equation for gv. As I do not know anything where you came up with gv or what it should be, that's the extent I can be of assistance on this matter. I merely ran a quick monte carlo simulation on a sizeable random distribution of v's from -1000 to +1000 and they all came back around R*T in their results.

HTH