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Machine {base}R Documentation

Machine Characteristics

Description

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.

The algorithm is based on Cody's subroutine MACHAR (see the reference below).

Usage

Machine()
.Machine

Value

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.

References

W. J. Cody (1988), MACHAR: A Subroutine to Dynamically Determine Machine Parameters. Transactions on Mathematical Software, 14, 4, 303-311.


[Package base version 0.60 ]