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## Copyright (C) 2005 Carl Osterwisch <osterwischc@asme.org>
## Copyright (C) 2013 CarnĂŤ Draug <carandraug@octave.org>
##
## This program is free software; you can redistribute it and/or modify it under
## the terms of the GNU General Public License as published by the Free Software
## Foundation; either version 3 of the License, or (at your option) any later
## version.
##
## This program is distributed in the hope that it will be useful, but WITHOUT
## ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
## FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
## details.
##
## You should have received a copy of the GNU General Public License along with
## this program; if not, see <http://www.gnu.org/licenses/>.
## -*- texinfo -*-
## @deftypefn {Function File} {} units (@var{fromUnit}, @var{toUnit})
## @deftypefnx {Function File} {} units (@var{fromUnit}, @var{toUnit}, @var{x})
## Return the conversion factor from @var{fromUnit} to @var{toUnit} measurements.
##
## This is an octave interface to the @strong{GNU Units} program which comes
## with an annotated, extendable database defining over two thousand
## measurement units. See @code{man units} or
## @url{http://www.gnu.org/software/units} for more information.
## If the optional argument @var{x} is supplied, return that argument
## multiplied by the conversion factor. For example, to
## convert three values from miles per hour into meters per second:
##
## @example
## units ("mile/hr", "m/sec", [30, 55, 75])
## ans =
##
## 13.411 24.587 33.528
## @end example
## @end deftypefn
function y = units (fromUnit, toUnit, x = 1)
if (nargin < 2 || nargin > 3)
print_usage ();
elseif (! ischar (fromUnit))
error ("units: FromUNIT must be a string");
elseif (! ischar (toUnit))
error ("units: ToUNIT must be a string");
elseif (! isnumeric (x))
error ("units: X must be numeric");
endif
persistent available = check_units ();
persistent compact = has_compact_option ();
persistent template = template_cmd (compact);
## We have to insert the template on the string this way, because it may have
## a %%.16g which we may want to keep for later use in non-linear conversion
cmd = sprintf ([template ' "%s" "%s"'], fromUnit, toUnit);
[status, rawoutput] = system (cmd);
if (status)
error ("units: %s", rawoutput);
endif
if (! compact)
## No compact or one-line option, we need to find the conversion factor
## from the text ourselves
ini_factor = index (rawoutput, "*");
end_factor = index (rawoutput, "\n") - 1;
if (isempty (ini_factor) || ini_factor > end_factor)
error ("units: unable to parse output from units:\n%s", rawoutput);
endif
rawoutput = rawoutput(ini_factor+1:end_factor);
endif
c_factor = str2double (rawoutput);
if (any (isnan (c_factor(:))))
if (index (rawoutput, "=") || index (rawoutput, "+") ||
index (rawoutput, "-") || index (rawoutput, "*") ||
index (rawoutput, "/"))
## If there's a mathematical operator in the output, it may be a formula
## for a non-linear conversion such as "tempC(x) = x K + stdtemp"
## We don't check for the equal only because some versions of units data
## file (not version of the units application, see bug #38270) have a
## very different syntax.
if (nargin < 3)
## for a non-linear unit conversion, we need a value to convert
error ("units: argument X is required for non-linear unit conversion");
endif
y = zeros (size (x));
template_non_linear = function_template (template, fromUnit, toUnit);
for ind = 1:numel(y)
cmd = sprintf (template_non_linear, x(ind));
[status, rawoutput] = system (cmd);
if (status)
error ("units: %s", rawoutput);
endif
y(ind) = str2double (rawoutput);
if (isnan (y(ind)))
error ("units unable to parse non-linear conversion `%s'", rawoutput);
endif
endfor
else
error ("units: unable to parse output `%s' from units.", rawoutput);
endif
else
y = x * c_factor;
endif
endfunction
function fpath = check_units ()
## See bug #38270 about why we're checking this way.
fpath = file_in_path (getenv ("PATH"), sprintf ("units%s", octave_config_info ("EXEEXT")));
if (isempty (fpath))
error ("units: %s\nVerify that GNU units is installed in the current path.",
rawoutput);
endif
endfunction
function compact = has_compact_option ()
compact = true;
## We must give some units to convert because the only thing that would
## make it not do any work (--version) actually exits with exit value 3
[status, rawoutput] = system ('units --compact --one-line "in" "cm"');
if (status)
compact = false;
endif
endfunction
function template = template_cmd (compact)
## do we have the format option?
format = true;
[status, rawoutput] = system ('units --output-format "%.16g" "in" "cm"');
if (status)
format = false;
endif
template = "units ";
if (format)
template = [template '--output-format "%%.16g" '];
endif
if (compact)
template = [template '--compact --one-line '];
endif
endfunction
## Test the correct way to do non-linear conversion.
function template = function_template (template, from, to)
## First try the most common syntax distributed with the most recent
## units.dat file using parentheses "from(x)" as if it was a function.
if (! system (sprintf ([template '"%s(1)" "%s"'], from, to), true))
template = sprintf ('%s "%s(%%.16g)" "%s"', template, from, to);
## If it doesn't work, try the oldest syntax of the style "x from"
elseif (! system (sprintf ([template '"100 %s" "%s"'], from, to), true))
template = sprintf ('%s "%%.16g %s" "%s"', template, from, to);
## If it doesn't work, give up
else
error ("units: unable to identify correct syntax for non-linear conversion");
endif
endfunction
%!demo
%! a.value = 100; a.unit = 'lb';
%! b.value = 50; b.unit = 'oz';
%! c.unit = 'kg';
%! c.value = units(a.unit, c.unit, a.value) + units(b.unit, c.unit, b.value)
# test normal usage
%!assert (units ("in", "mm"), 25.4)
# multiple values
%!assert (units ("in", "mm", [5 7; 8 9]), 25.4 * [5 7; 8 9])
# a non-linear conversion
%!assert (units ("tempC", "tempF", 100), 212)
%!error <non-linear unit conversion> units ("tempC", "tempF")

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