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Topic: digit-precision for gaussian inputs converting cartesian matrix from
Replies: 2   Last Post: Dec 5, 2012 3:10 AM

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locometro, INMETRO/UFRJ, Brasil - RJ

Posts: 5
Registered: 11/11/12
Re: digit-precision for gaussian inputs converting cartesian matrix from
Posted: Dec 5, 2012 3:10 AM
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Bill,

Thanks for the suggestions!


Em segunda-feira, 3 de dezembro de 2012 06h37min55s UTC-2, Bill Rowe escreveu:
> On 11/30/12 at 5:59 AM, decicco10@gmail.com (locometro, INMETRO/UFRJ,
>
> Brasil - RJ) wrote:
>
>
>

> >I have some issues to discuss here:
>
>
>

> >My goal: rotation,x-y plane, apllying over some cartesians vectors.
>
>
>

> >(*step 1: I import a input.txt for Gaussian program like this: *)
>
>
>

> >%chk=campoX_1.chk %mem=2gb %nproc=4
>
> >#p b3lyp/6-31+g(d,p) geom=connectivity field=x+1 pop=reg
>
> >#int=ultrafine
>
>
>

> >single point campo direcao X+01
>
>
>

> >0 1
>
> >C 0.00000000 0.00000000 0.00000000
>
> >C 1.41786969 0.00000000 0.00000000
>
> >C -0.68401407 1.24221249 0.00000000
>
> >etc...(72lines).
>
>
>

> >(*step 2: I extract the data from input above, as below:*)
>
>
>

> >data2 = Take[data1, {9, 56}, {2, 4}]] data3 = Flatten[Take[data1,
>
> >{9, 56}, {1}]]; data4 = Drop[data1, {8, 56}, None];
>
>
>

> >(*As I need the 1st(molecules symbol), 2nd (X) , 3rd (Y) and 4th(Z)
>
> >columns, for my table and calculations*).
>
>
>

> >(*step 3: Rotation 45 degree, over plane x-y, using the exctracted
>
> >columns*)
>
>
>

> >rotZ = RotationMatrix[45 Degree, {0, 0, 1}]; datarotZ = (rotZ.#) &
>
> >/@ data2 (*this promote the rotation matrice over x-y-x*)
>
>
>

> >output-> {{0., 0., 0.}, {1.00259, 1.00259, 0.}, {-1.36205, 0.394706,
>
> >0.}, {-2.49436, 0.668808, 0.00086376}, {1.85795, 1.79358,
>
> >-0.00004936}, {-3.36958, -5.96549, -0.00908542}, \
>
> >{-2.95205, -7.30672, 0.00803008},...etc (* cartesians numbers
>
> >already rotated 45 degrees*).
>
>
>

> >BUT NOTICE that the numbers of digits has been modified!, I need the
>
> >original 8 digits, including zeros, after the decimal point! I do
>
> >not want mathematica aplying any aproximation or cuts.
>
>
>
> There are a couple of issues here. First, any number entered
>
> with a decimal point and not given an explicit precision is a
>
> machine precision number in Mathematica. All machine precision
>
> numbers are stored as binary data. In general, numbers you enter
>
> as decimal numbers cannot be represented exactly in a finite
>
> number of binary digits. So, the value Mathematica uses
>
> typically is slightly different than the value you entered.
>
>
>
> Once you start using machine precision values, by default
>
> Mathematica will use machine precision for other parts of you
>
> computation. These values also will be slightly different than
>
> what you enter. As the computation proceeds these small
>
> differences accumulate. The end result is reversing computations
>
> often will not result in exactly the same decimal digits even
>
> though the reverse computation would mathematically be an exact
>
> inverse, resulting in an identity operation.
>
>
>
> The only way around this issue is to either use exact values (no
>
> decimal point, all fractions expressed as rationals) or to
>
> increase the precision in the values you enter to make use of
>
> Mathematica's arbitrary precision arithmetic. The cost is slower
>
> execution of computations.
>
>
>
> A second issue is by default Mathematica doesn't display
>
> trailing zeros. You can change this by changing your display
>
> options or by using functions like NumberForm to control how
>
> Mathematica displays numbers.






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