NaN issue when calculating for a mean value

Question

Kira Bruce 2020-1-23

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/501678-nan-issue-when-calculating-for-a-mean-value

编辑： Guillaume 2020-1-23

gh = 0;
fg = 1; 
mu_fg = MU_fib/fg;  
adi = 1; 
w = 0.042;
for ix = 1:200 
    for iy = 1:200
        gh = gh + 1;
        D = phi.*exp(MU_fat).*mu_fg.*((1-exp(-mewelement.*w))/mewelement).*((fg+adi)/adi).*(1/w);
        meanD = sum(D)/60;
    end 

Above is a section of the program I am writing. This section has the goal of find the dose for each section of tissue. However, when i run it through, I get dose as NaN. I want the mean dose for the entire phantom as a single number.

Without the line meanD = sum(D)/60;, I get a matrix of 1 x 60 values which i don't want. I want one value for the dose (D).

Thank you. Any help is appreciated

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Guillaume 2020-1-23

编辑：Guillaume 2020-1-23

Unfortunately, we don't know what MU_fib, MU_fat, phi and mwelement are, so can't test your code. You're getting NaN because one of your expression result in either

0 / 0
Inf / Inf
0 * Inf
Inf - Inf or similar operation

or one of your input is NaN already.

"I get a matrix of 1 x 60 values which i don't want" If you didn't expect a vector, then clearly you've got a bug. You'll get a vector if any of the above variables are a vector.

Note that as written, your loops overwrite meanD and D at each step, so you'll end up with just the value for ix = 200 and iy = 200 at the end.

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