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Getting Nan after using expm

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raha ahmadi
raha ahmadi on 1 Jun 2021
Commented: raha ahmadi on 1 Jun 2021
Hi H dont know why I get Nan in situatin A but not in B.
Thanks in advance
% situation A
r=[1e5,0,0;
0,-2e5,0;
1,1,-5e5]
R=expm(r);
%% situation B
g=[-1e5,0,0;
0,-2e5,0;
1,1,-5e5]
G=expm(g);

Accepted Answer

Jan
Jan on 1 Jun 2021
See the help text of expm:
Although it is not computed this way, if A has a full set of eigenvectors V with corresponding eigenvalues D then
% [V,D] = EIG(A) and expm(A) = V*diag(exp(diag(D)))/V
r=[1e5,0,0; 0,-2e5,0; 1,1,-5e5];
exp(diag(D))
% [0; Inf; 0]
This Inf is the cause of the NaN output.
  1 Comment
raha ahmadi
raha ahmadi on 1 Jun 2021
I really appreciate for your quick response. In fact I expect Inf instead of NaN
Wish you all the best

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R2018b

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