Exponential of very large number

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Teshome Kumsa
Teshome Kumsa on 28 Aug 2021
Commented: Steven Lord on 28 Aug 2021
Hello all! I was trying to calculate exponental of some vectors. Actually my vector has very big entries(each entries are Stresses accumulated during earquakes. That is why they are very big).
For example
exp([-235628865.417257 29372700213.5032]/10.^5)
It returns ans=
0 Inf
I need a comment on it.
  1 Comment
Matt J
Matt J on 28 Aug 2021
It wouldn't make sense to take exp() to any greater precision unless you are going to take the log of it later.

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Answers (1)

Chunru
Chunru on 28 Aug 2021
Edited: Chunru on 28 Aug 2021
Those number are beyond the scope of double numbers. You can try vpa. Alternatively, keep track of the mantisa and exponent yourself as follows:
a=log10(exp(1))*([-235628865.417257 29372700213.5032]/10.^5);
aint = ceil(a);
afrac = a -aint;
xm = 10.^afrac;
xe = aint;
xstr = xm(:)+" x 10 ^ "+xe(:)
xstr = 2×1 string array
"0.47516 x 10 ^ -1023" "0.1038 x 10 ^ 127565"
  3 Comments
Chunru
Chunru on 28 Aug 2021
The code uses your edited numbers now.
Steven Lord
Steven Lord on 28 Aug 2021
What are you hoping to do with those answers? Are you planning on dividing them by exp(x) for some other value of large magnitude?

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