very big or small det of a matrix

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Wojciech
Wojciech 2011-12-16
Determinant i.e. det(x) in som cases computes very small or very big numbers. Matlab displays them as zero, but I know that thery are below 10e-300 (Im not sure is it 300 or 312?= or above 10e300. I see them as zero but If I change parameters I got e.g. 1837363e-277. Is it possible to change the range of displaying and achieve numbers smaller than 10e-300 ?

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Jan
Jan 2011-12-16
Using:
format long g
numbers until 2.2250738585072e-308 are displayed. See realmin.
But I'd be extremly careful if a determinant has such a small value: Due to rounding errors it is hard to estimate if this value is reliable.
  2 个评论
Wojciech
Wojciech 2011-12-16
Thanks. In such case the value should be recognized as zero, shouldnt it?
But what about large numbers? Infinity? Regards
Jan
Jan 2011-12-16
While a determinant can get very small due to cancelation errors, they cannot grow by accident. The upper limit of the value is limited by the values of the elements of the matrix.

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