/usr/share/octave/packages/interval-2.1.0/@infsup/norm.m is in octave-interval 2.1.0-2.
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##
## 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 -*-
## @documentencoding UTF-8
## @defmethod {@@infsup} norm (@var{A}, @var{P})
## @defmethodx {@@infsup} norm (@var{A}, @var{P}, @var{Q})
## @defmethodx {@@infsup} norm (@var{A}, @var{P}, @var{OPT})
##
## Compute the p-norm (or p,q-norm) of the matrix @var{A}.
##
## If @var{A} is a matrix:
## @table @asis
## @item @var{P} = 1
## 1-norm, the largest column sum of the absolute values of @var{A}.
## @item @var{P} = inf
## Infinity norm, the largest row sum of the absolute values of @var{A}.
## @item @var{P} = "fro"
## Frobenius norm of @var{A}, @code{sqrt (sum (diag (@var{A}' * @var{A})))}.
## @end table
##
## If @var{A} is a vector or a scalar:
## @table @asis
## @item @var{P} = inf
## @code{max (abs (@var{A}))}.
## @item @var{P} = -inf
## @code{min (abs (@var{A}))}.
## @item @var{P} = "fro"
## Frobenius norm of @var{A}, @code{sqrt (sumsq (abs (A)))}.
## @item @var{P} = 0
## Hamming norm - the number of nonzero elements.
## @item other @var{P}, @code{@var{P} > 1}
## p-norm of @var{A}, @code{(sum (abs (@var{A}) .^ @var{P})) ^ (1/@var{P})}.
## @item other @var{P}, @code{@var{P} < 1}
## p-pseudonorm defined as above.
## @end table
##
## It @var{Q} is used, compute the subordinate matrix norm induced by the
## vector p-norm and vector q-norm. The subordinate p,q-norm is defined as the
## maximum of @code{norm (@var{A} * @var{x}, @var{Q})}, where @var{x} can be
## chosen such that @code{norm (@var{x}, @var{P}) = 1}. For @code{@var{P} = 1}
## and @code{@var{Q} = inf} this is the max norm,
## @code{max (max (abs (@var{A})))}.
##
## If @var{OPT} is the value "rows", treat each row as a vector and compute its
## norm. The result returned as a column vector. Similarly, if @var{OPT} is
## "columns" or "cols" then compute the norms of each column and return a row
## vector.
##
## Accuracy: The result is a valid enclosure.
##
## @example
## @group
## norm (infsup (magic (3)), "fro")
## @result{} ans ⊂ [16.881, 16.882]
## @end group
## @group
## norm (infsup (magic (3)), 1, "cols")
## @result{} ans = 1×3 interval vector
##
## [15] [15] [15]
##
## @end group
## @end example
## @seealso{@@infsup/abs, @@infsup/max}
## @end defmethod
## Author: Oliver Heimlich
## Keywords: interval
## Created: 2016-01-26
function result = norm (A, p, opt)
if (nargin > 3 || not (isa (A, "infsup")))
print_usage ();
return
endif
if (nargin < 2)
p = 2;
opt = "";
elseif (nargin < 3)
opt = "";
endif
if (strcmp (p, "inf"))
p = inf;
endif
switch (opt)
case "rows"
dim = 2;
case {"columns", "cols"}
dim = 1;
case ""
if (isvector (A.inf))
## Try to find non-singleton dimension
dim = find (size (A.inf) > 1, 1);
if (isempty (dim))
dim = 1;
endif
else
dim = [];
endif
otherwise
## Subordinate p,q matrix norm
q = opt;
dim = [];
if (strcmp (q, "inf"))
q = inf;
endif
if (p == 1 && q == inf)
## Max norm
result = max (max (abs (A)));
return
elseif (p == 1 && q == 1)
## 1-norm, computed below
elseif (p == inf && q == inf)
## inf-norm, computed below
elseif (p == inf && q == 1)
## inf,1-norm
## Computation via z' * A * y
## with y and z being vectors of -1 and 1 entries.
## Important papers by Jiří Rohn
##
## Computing the Norm || A ||_{inf,1} is NP-Hard
## Linear and Multilinear Algebra 47 (2000), 195-204.
## http://dx.doi.org/10.1080/03081080008818644
## http://uivtx.cs.cas.cz/~rohn/publist/norm.pdf
##
## R. Farhadsefat, J. Rohn and T. Lotfi,
## Norms of Interval Matrices.
## Technical Report No. 1122, Institute of Computer Science,
## Academy of Sciences of the Czech Republic, Prague 2011.
## http://www3.cs.cas.cz/ics/reports/v1122-11.pdf
## http://uivtx.cs.cas.cz/~rohn/publist/normlaa.pdf
result = 0;
## Unfortunately this is NP-hard
# 2^n different logical vectors of length n
y = dec2bin ((1 : pow2 (columns (A)))' - 1) == '1';
# 2^m different logical vectors of length m
z = dec2bin ((1 : pow2 (rows (A)))' - 1) == '1';
for i = 1 : rows (y)
idx = substruct ("()", {":", y(i, :)});
B = subsasgn (A, idx, ...
uminus (subsref (A, idx)));
for j = 1 : rows (z)
idx = substruct ("()", {z(j, :), ":"});
C = subsasgn (B, idx, ...
uminus (subsref (B, idx)));
result = max (result, sum (vec (C)));
endfor
endfor
return
else
error ("norm: Particular option or p,q-norm is not yet supported")
endif
endswitch
if (isempty (dim))
## Matrix norm
switch (p)
case 1
result = max (sum (abs (A), 1));
case inf
result = max (sum (abs (A), 2));
case "fro"
result = sqrt (sumsq (vec (A)));
otherwise
error ("norm: Particular matrix norm is not yet supported")
endswitch
else
## Vector norm
switch (p)
case inf
result = max (abs (A), [], dim);
case -inf
result = min (abs (A), [], dim);
case {"fro", 2}
result = sqrt (sumsq (A, dim));
case 0
## Hamming norm: the number of non-zero elements
result = sum (subsasgn (subsasgn (subsasgn (A, ...
substruct ("()", {ismember(0, A)}), "[0, 1]"), ...
substruct ("()", {A == 0}), 0), ...
substruct ("()", {A > 0 | A < 0}), 1), ...
dim);
otherwise
warning ("off", "interval:ImplicitPromote", "local");
result = (sum (abs (A) .^ p, dim)) .^ (1 ./ infsup (p));
endswitch
endif
endfunction
%!test
%! A = infsup ("0 [Empty] [0, 1] 1");
%! assert (isequal (norm (A, 0, "cols"), infsup ("0 [Empty] [0, 1] 1")));
%!assert (norm (infsup (magic (3)), inf, 1) == 45);
%!assert (norm (infsup (-magic (3), magic (3)), inf, 1) == "[0, 45]");
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