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Round matrix elements to lower precision in MATLAB
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chop.m
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readme.md

Chop - MATLAB code for rounding matrix elements to lower precision

About

chop is a MATLAB function for rounding the elements of a matrix to a lower precision arithmetic with one of several forms of rounding. Its intended use is for simulating arithmetic of different precisions (less than double) with various rounding modes. The input to chop should be single precision or double precision and the output will have the same type: the lower precision numbers are stored within a higher precision type.

The arithmetic formats supported are

  • 'b', 'bfloat16' - bfloat16,
  • 'h', 'half', 'fp16' - IEEE half precision (the default),
  • 's', 'single', 'fp32' - IEEE single precision,
  • 'd', 'double', 'fp64' - IEEE double precision,
  • 'c', 'custom' - custom format.

Subnormal numbers can be supported or not, and in the latter case they are flushed to zero.

Several rounding modes are supported:

  • Round to nearest using round to even last bit to break ties (the default).
  • Round towards plus infinity (round up).
  • Round towards minus infinity (round down).
  • Round towards zero.
  • Stochastic rounding - round to the next larger or next smaller floating-point number with probability proportional to the distance to those floating-point numbers.
  • Stochastic rounding - round to the next larger or next smaller floating-point number with equal probability.

A further option causes each element of the rounded result to have, with a specified probability defaulting to 0.5, a randomly chosen bit in its significand flipped.

Demonstration function:

  • demo-harmonic computes the harmonic series in several arithmetic formats using all the supported rounding modes.

Other M-file:

  • roundit is a function for rounding a matrix to have integer entries. It is used by chop and is not intended to be called directly.

Test functions:

  • test_chop is a test function for chop.
  • test_roundit is a test function for roundit.

Each test function should print "All tests successful!".

The function chop is a successor to a function of the same name in the The Matrix Computation Toolbox (also available on File Exchange).

Requirements

The code was developed in MATLAB R2018b and works with versions at least back to R2016a.

Reference

Nicholas J. Higham and Srikara Pranesh, Simulating Low Precision Floating-Point Arithmetic, MIMS Eprint 2019.4, Manchester Institute for Mathematical Sciences, The University of Manchester, UK, March 2019.

License

See license.txt for licensing information.

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