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// SPDX-License-Identifier: Apache-2.0
//
// Copyright 2008-2016 Conrad Sanderson (http://conradsanderson.id.au)
// Copyright 2008-2016 National ICT Australia (NICTA)
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// ------------------------------------------------------------------------
//! \addtogroup fn_inplace_strans
//! @{
template<typename eT>
inline
void
inplace_strans
(
Mat<eT>& X,
const char* method = "std"
)
{
arma_extra_debug_sigprint();
const char sig = (method != nullptr) ? method[0] : char(0);
arma_debug_check( ((sig != 's') && (sig != 'l')), "inplace_strans(): unknown method specified" );
const bool low_memory = (sig == 'l');
if( (low_memory == false) || (X.n_rows == X.n_cols) )
{
op_strans::apply_mat_inplace(X);
}
else
{
// in-place algorithm inspired by:
// Fred G. Gustavson, Tadeusz Swirszcz.
// In-Place Transposition of Rectangular Matrices.
// Applied Parallel Computing. State of the Art in Scientific Computing.
// Lecture Notes in Computer Science. Volume 4699, pp. 560-569, 2007.
// X.set_size() will check whether we can change the dimensions of X;
// X.set_size() will also reuse existing memory, as the number of elements hasn't changed
X.set_size(X.n_cols, X.n_rows);
const uword m = X.n_cols;
const uword n = X.n_rows;
std::vector<bool> visited(X.n_elem); // TODO: replace std::vector<bool> with a better implementation
for(uword col = 0; col < m; ++col)
for(uword row = 0; row < n; ++row)
{
const uword pos = col*n + row;
if(visited[pos] == false)
{
uword curr_pos = pos;
eT val = X.at(row, col);
while(visited[curr_pos] == false)
{
visited[curr_pos] = true;
const uword j = curr_pos / m;
const uword i = curr_pos - m * j;
const eT tmp = X.at(j, i);
X.at(j, i) = val;
val = tmp;
curr_pos = i*n + j;
}
}
}
}
}
//! @}
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