89 lines
2.2 KiB
C++
89 lines
2.2 KiB
C++
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// Copyright (C) 2013 National ICT Australia (NICTA)
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//
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// This Source Code Form is subject to the terms of the Mozilla Public
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// License, v. 2.0. If a copy of the MPL was not distributed with this
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// file, You can obtain one at http://mozilla.org/MPL/2.0/.
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// -------------------------------------------------------------------
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//
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// Written by Conrad Sanderson - http://conradsanderson.id.au
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// Written by Alexandre Drouin
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//! \addtogroup fn_inplace_strans
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//! @{
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template<typename eT>
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inline
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void
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inplace_strans
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(
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Mat<eT>& X,
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const char* method = "std"
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)
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{
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arma_extra_debug_sigprint();
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const char sig = (method != NULL) ? method[0] : char(0);
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arma_debug_check( ((sig != 's') && (sig != 'l')), "inplace_strans(): unknown method specified" );
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const bool low_memory = (sig == 'l');
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if( (low_memory == false) || (X.n_rows == X.n_cols) )
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{
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op_strans::apply_mat_inplace(X);
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}
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else
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{
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// in-place algorithm inspired by:
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// Fred G. Gustavson, Tadeusz Swirszcz.
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// In-Place Transposition of Rectangular Matrices.
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// Applied Parallel Computing. State of the Art in Scientific Computing.
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// Lecture Notes in Computer Science. Volume 4699, pp. 560-569, 2007.
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// X.set_size() will check whether we can change the dimensions of X;
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// X.set_size() will also reuse existing memory, as the number of elements hasn't changed
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X.set_size(X.n_cols, X.n_rows);
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const uword m = X.n_cols;
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const uword n = X.n_rows;
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std::vector<bool> visited(X.n_elem); // TODO: replace std::vector<bool> with a better implementation
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for(uword col = 0; col < m; ++col)
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for(uword row = 0; row < n; ++row)
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{
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const uword pos = col*n + row;
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if(visited[pos] == false)
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{
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uword curr_pos = pos;
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eT val = X.at(row, col);
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while(visited[curr_pos] == false)
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{
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visited[curr_pos] = true;
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const uword j = curr_pos / m;
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const uword i = curr_pos - m * j;
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const eT tmp = X.at(j, i);
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X.at(j, i) = val;
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val = tmp;
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curr_pos = i*n + j;
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}
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}
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}
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}
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}
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//! @}
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