Why do I get NAN?

Question

Yasmin Tamimi 2014-1-19

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/112933-why-do-i-get-nan

评论： Dheeraja Karthikeyan 2020-4-25

采纳的回答： Roger Stafford

在 MATLAB Online 中打开

Hey everyone,

I'm running this equation

hMphi(1) = - (dd_Anis(1) * ddu_acos(1) * du_dMphi(1))/(C2*sin(Mtheta(1)))- ((Is*P_hbar/(2*P_Q*g*C2))*((ephix(1)*Ffx(1))+(ephiy(1)*Ffy(1))))- Ms*(Ny-Nx)*sin(Mtheta(1))*sin(2*Mphi(1))+ (Happy*cos(Mphi(1)) - Happx*sin(Mphi(1))) ;

in a loop and a certain point the value of this vector becomes a NAN?! Can Anyone tell me why is this happening? I' dividing by a sin, so I thought that maybe the problem is from it, but I printed the values of it I didn't get Inf.

Thanks

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Answer 1

Roger Stafford 2014-1-19

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https://ww2.mathworks.cn/matlabcentral/answers/112933-why-do-i-get-nan#answer_121415

Any of these arithmetic operations will produce a NaN: zero/zero, zero*infinity, infinity/infinity, infinity-infinity. For example, if any of the three quantities, dd_Anis, ddu_acos, or du_dMph were to become zero at the same time that sin(Mtheta) is zero, that would produce a NaN. You should make a test on hMphi each time it is computed and arrange to stop if a NaN is detected so you can check all the values that go into your equation at that point.

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Answer 2

Jan 2014-1-19

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https://ww2.mathworks.cn/matlabcentral/answers/112933-why-do-i-get-nan#answer_121417

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You can stop the code automatically, when the NaN appears:

dbstop if naninf

Then inspect the local variables and evaluate the different parts of the equation in the command window until you find the reason for the NaN.

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Dheeraja Karthikeyan 2020-4-25

Thanks a lot for this! You were a blessing in disguise!

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Answer 3

Anna 2014-1-19

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https://ww2.mathworks.cn/matlabcentral/answers/112933-why-do-i-get-nan#answer_121409

Have you tried to isolate the part of the equation where the fault is at? Debug the equation in the loop iteration before the equation turns into a NaN.