.Machine {base}R Documentation

Numerical Characteristics of the Machine

Description

.Machine is a variable holding information on the numerical characteristics of the machine R is running on, such as the largest double or integer and the machine's precision.

Usage

.Machine

Details

The algorithm is based on Cody's (1988) subroutine MACHAR.

Value

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.
sizeof.long the number of bytes in a C long type.
sizeof.longlong the number of bytes in a C long long type. Will be zero if there is no such type.
sizeof.longdouble the number of bytes in a C long double type. Will be zero if there is no such type.
sizeof.pointer the number of bytes in a C SEXP type.

References

Cody, W. J. (1988) MACHAR: A subroutine to dynamically determine machine parameters. Transactions on Mathematical Software, 14, 4, 303–311.

See Also

.Platform for details of the platform.

Examples

.Machine
## or for a neat printout
noquote(unlist(format(.Machine)))

[Package base version 2.1.0 Index]