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Discussion Groups | Matlab DSP | what's the smallest real positive number in Matlab?

Technical discussion about Matlab and issues related to Digital Signal Processing.

  

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what's the smallest real positive number in Matlab? - Lan Wang - Jul 4 1:12:00 2003

Hi Folks,

As a new user of Matlab, I'm puzzled by the following two questions:

1. I typed "realmin" in the command window and it gave me 2.2251e-308,
but why did I get a matrix with a determinant equal to
5.434722e-322? I used "fprintf("%e", d)" to print the determinant.

2. In my result, DETERMINANT = 0.000000E+000 occurred for a
matrix, which is zero in Matlab (and I verified it), why was there no
error message, nor warning, coming up when the matrix with this
determinant was inverted in my program? (But in the command
window, when I tried to invert an obvioulsy singular matrix, the error
message "Warning: Matrix is singular to working precision." showed
up.)

Many thanks.

Richard







Re: what's the smallest real positive number in Matlab? - Nandakishore Ramaswamy - Jul 6 0:48:00 2003

Regarding your 2nd question the warning does show up but the answer comes up as
"Inf" which I suppose is infinity.
-Nandakishore Lan Wang <> wrote:Hi Folks,

As a new user of Matlab, I'm puzzled by the following two questions:

1. I typed "realmin" in the command window and it gave me 2.2251e-308,
but why did I get a matrix with a determinant equal to
5.434722e-322? I used "fprintf("%e", d)" to print the determinant.

2. In my result, DETERMINANT = 0.000000E+000 occurred for a
matrix, which is zero in Matlab (and I verified it), why was there no
error message, nor warning, coming up when the matrix with this
determinant was inverted in my program? (But in the command
window, when I tried to invert an obvioulsy singular matrix, the error
message "Warning: Matrix is singular to working precision." showed
up.)

Many thanks.

Richard
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Re: what's the smallest real positive number in Matlab? - Pavel Jiranek - Jul 6 15:00:00 2003

Make sure if you're working with single or double precission. Paya

Lan Wang wrote:

>Hi Folks,
>
>As a new user of Matlab, I'm puzzled by the following two questions:
>
>1. I typed "realmin" in the command window and it gave me 2.2251e-308,
> but why did I get a matrix with a determinant equal to
> 5.434722e-322? I used "fprintf("%e", d)" to print the determinant.
>
>2. In my result, DETERMINANT = 0.000000E+000 occurred for a
> matrix, which is zero in Matlab (and I verified it), why was there no
> error message, nor warning, coming up when the matrix with this
> determinant was inverted in my program? (But in the command
> window, when I tried to invert an obvioulsy singular matrix, the error
> message "Warning: Matrix is singular to working precision." showed
> up.)
>
>Many thanks.
>
>Richard







Re: what's the smallest real positive number in Matlab? - navaneetha krishnan - Jul 7 18:34:00 2003

Regarding question 1, it is possible to have values
less than realmin. These are called denormals and can
be as low as eps*realmin. See
http://www.mathworks.com/company/newsletter/pdf/Fall96Cleve.pdf
for details.

On question 2, make sure warnings are not switched off
in your program.

Navan

--- Lan Wang <> wrote:
> Hi Folks,
>
> As a new user of Matlab, I'm puzzled by the
> following two questions:
>
> 1. I typed "realmin" in the command window and it
> gave me 2.2251e-308,
> but why did I get a matrix with a determinant
> equal to
> 5.434722e-322? I used "fprintf("%e", d)" to print
> the determinant.
>
> 2. In my result, DETERMINANT = 0.000000E+000
> occurred for a
> matrix, which is zero in Matlab (and I verified
> it), why was there no
> error message, nor warning, coming up when the
> matrix with this
> determinant was inverted in my program? (But in
> the command
> window, when I tried to invert an obvioulsy
> singular matrix, the error
> message "Warning: Matrix is singular to working
> precision." showed
> up.)
>
> Many thanks.
>
> Richard
__________________________________