| Machine {base} | R Documentation |
Machine() returns information on numeric characteristics of the
machine R is running on, such as the largest double or integer and the
machine's precision.
.Machine is a variable holding this information.
Machine() .Machine
The algorithm is based on Cody's (1988) subroutine MACHAR.
Machine() returns a list with components (for simplicity, the
prefix ``double'' is omitted in the explanations)
double.eps |
the smallest positive floating-point number
x such that 1 + x != 1. It equals
base^ulp.digits if either base is 2 or rounding
is 0; otherwise, it is (base^ulp.digits) / 2. |
double.neg.eps |
a small positive floating-point number x
such that 1 - x != 1. It equals base^neg.ulp.digits
if base is 2 or round is 0; otherwise, it is
(base^neg.ulp.digits) / 2.
As neg.ulp.digits is bounded below by -(digits + 3),
neg.eps may not be the smallest number that can alter 1 by
subtraction. |
double.xmin |
the smallest non-vanishing normalized
floating-point power of the radix, i.e., base^min.exp. |
double.xmax |
the largest finite floating-point number.
Typically, it is equal to (1 - neg.eps) * base^max.exp, but
on some machines it is only the second, or perhaps third, largest
number, being too small by 1 or 2 units in the last digit of the
significand. |
double.base |
the radix for the floating-point representation |
double.digits |
the number of base digits in the floating-point significand |
double.rounding |
the rounding action. 0 if floating-point addition chops; 1 if floating-point addition rounds, but not in the IEEE style; 2 if floating-point addition rounds in the IEEE style; 3 if floating-point addition chops, and there is partial underflow; 4 if floating-point addition rounds, but not in the IEEE style, and there is partial underflow; 5 if floating-point addition rounds in the IEEE style, and there is partial underflow |
double.guard |
the number of guard digits for multiplication
with truncating arithmetic. It is 1 if floating-point arithmetic
truncates and more than digits base base digits
participate in the post-normalization shift of the floating-point
significand in multiplication, and 0 otherwise. |
double.ulp.digits |
the largest negative integer i such
that 1 + base^i != 1, except that it is bounded below by
-(digits + 3). |
double.neg.ulp.digits |
the largest negative integer i
such that 1 - base^i != 1, except that it is bounded below by
-(digits + 3). |
double.exponent |
the number of bits (decimal places if base is 10) reserved
for the representation of the exponent (including the bias or sign)
of a floating-point number |
double.min.exp |
the largest in magnitude negative integer i such that
base ^ i is positive and normalized. |
double.max.exp |
the smallest positive power of base that overflows. |
integer.max |
the largest integer which can be represented. |
Cody, W. J. (1988) MACHAR: A subroutine to dynamically determine machine parameters. Transactions on Mathematical Software, 14, 4, 303–311.
machine to determine the computer type which R is running on.
str(Machine()) 1 + .Machine$double.eps != 1 1 + .5* .Machine$double.eps == 1