From eda5bc26f44ee9a6f83dcf8c91f17296d7fc509d Mon Sep 17 00:00:00 2001
From: Nao Pross <np@0hm.ch>
Date: Mon, 12 Feb 2024 14:52:43 +0100
Subject: Move into version control

---
 .../include/armadillo_bits/fn_inplace_strans.hpp   | 95 ++++++++++++++++++++++
 1 file changed, 95 insertions(+)
 create mode 100644 src/armadillo/include/armadillo_bits/fn_inplace_strans.hpp

(limited to 'src/armadillo/include/armadillo_bits/fn_inplace_strans.hpp')

diff --git a/src/armadillo/include/armadillo_bits/fn_inplace_strans.hpp b/src/armadillo/include/armadillo_bits/fn_inplace_strans.hpp
new file mode 100644
index 0000000..ad09cf2
--- /dev/null
+++ b/src/armadillo/include/armadillo_bits/fn_inplace_strans.hpp
@@ -0,0 +1,95 @@
+// 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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