[R] what is R equivalent of Fortran DOUBLE PRECISION ?

[Steven McKinney]

>From the help page for "Foreign"
> ?Foreign


 Numeric vectors in R will be passed as type double * to C (and as double precision to Fortran)


Also, see the help page for "double"

> ?double

 R has no single precision data type. All real numbers are stored in double precision format. 
 The functions as.single and single are identical to as.double and double except they set 
 the attribute Csingle that is used in the .C and .Fortran interface, and they are intended 
 only to be used in that context.

HTH

Steven McKinney, Ph.D.

Statistician
Molecular Oncology and Breast Cancer Program
British Columbia Cancer Research Centre

email: smckinney +at+ bccrc +dot+ ca

tel: 604-675-8000 x7561

BCCRC
Molecular Oncology
675 West 10th Ave, Floor 4
Vancouver B.C. 
V5Z 1L3
Canada




-----Original Message-----
From: r-help-bounces at r-project.org on behalf of mauede at alice.it
Sent: Mon 3/30/2009 3:07 AM
To: r-help at r-project.org
Cc: John C.  Nash
Subject: [R] what is R equivalent of Fortran DOUBLE PRECISION ?
 
I noticed taht R cannot understand certain Fortran real constant formats. For instance:

 c14    <- as.double( 7.785205408500864D-02)
Error: unexpected symbol in " c14    <- as.double( 7.785205408500864D"

The above "D" is used in Fortran language to indicate the memory starage mode. That is for instructing Fortran compiler 
to store such a REAL constant in  DOUBLE PRECISION... am I right ?
Since R cannot undestand numerical conatant post-fixed by the letter "D", I wonder how I can instruct R interpreter to 
store such a numerical constant reserving as muh memory as necessary so as to accommodate a double precision number.

I noticed R accepts the folllowing syntax but I do not know if i have achieved my goal thsi way:

>  c14    <- as.double( 7.785205408500864E-02)
> typeof(c4)
[1] "double"

My questions are: what is the best precision I can get with R when dealing with real number ?
Is R "double" type equvalent to Fortran DOUBLE PRECISION  for internal number representation ?

Thank you very much.
Maura








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