From cca66b9ec4e494c1d919bff0f71a820d8afab1fa Mon Sep 17 00:00:00 2001
From: Daniel Baumann <daniel.baumann@progress-linux.org>
Date: Sun, 7 Apr 2024 20:24:48 +0200
Subject: Adding upstream version 1.2.2.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
---
 .../adaptagrams/libcola/conjugate_gradient.cpp     | 137 +++++++++++++++++++++
 1 file changed, 137 insertions(+)
 create mode 100644 src/3rdparty/adaptagrams/libcola/conjugate_gradient.cpp

(limited to 'src/3rdparty/adaptagrams/libcola/conjugate_gradient.cpp')

diff --git a/src/3rdparty/adaptagrams/libcola/conjugate_gradient.cpp b/src/3rdparty/adaptagrams/libcola/conjugate_gradient.cpp
new file mode 100644
index 0000000..adb7fa6
--- /dev/null
+++ b/src/3rdparty/adaptagrams/libcola/conjugate_gradient.cpp
@@ -0,0 +1,137 @@
+/*
+ * vim: ts=4 sw=4 et tw=0 wm=0
+ *
+ * libcola - A library providing force-directed network layout using the 
+ *           stress-majorization method subject to separation constraints.
+ *
+ * Copyright (C) 2006  Nathan Hurst <njh@njhurst.com>
+ * Copyright (C) 2006-2008  Monash University
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ * See the file LICENSE.LGPL distributed with the library.
+ *
+ * This library 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.  
+ *
+ * Author(s):  Nathan Hurst
+ *             Tim Dwyer
+ *            
+*/
+
+
+#include <cmath>
+#include <cstdlib>
+#include <cassert>
+#include <valarray>
+
+#include "libvpsc/assertions.h"
+#include "libcola/commondefs.h"
+#include "libcola/conjugate_gradient.h"
+
+/* lifted wholely from wikipedia.  Well, apart from the bug in the wikipedia version. */
+
+using std::valarray;
+
+static void 
+matrix_times_vector(valarray<double> const &matrix, /* m * n */
+            valarray<double> const &vec,  /* n */
+            valarray<double> &result) /* m */
+{
+    unsigned n = vec.size();
+    unsigned m = result.size();
+    COLA_ASSERT(m*n == matrix.size());
+#   if defined(_MSC_VER)
+    // magmy: The following lines show how operator[] is defined for valarray under MSVC
+    // _Ty valarray<_Ty>::operator[](size_t _Off) const;
+    // _Ty &valarray<_Ty>::operator[](size_t _Off);
+    // As a consequence, it is not possible to take the address of a constant valarray[n].
+    // This looks like a bug in the Microsoft's <valarray> file.
+    // Below is a workaround
+    double const *mp = &const_cast<valarray<double> &>(matrix)[0];
+#   else
+    const double* mp = &matrix[0];
+#   endif
+    for (unsigned i = 0; i < m; i++) {
+        double res = 0;
+        for (unsigned j = 0; j < n; j++)
+            res += *mp++ * vec[j];
+        result[i] = res;
+    }
+}
+
+/*
+static double Linfty(valarray<double> const &vec) {
+    return std::max(vec.max(), -vec.min());
+}
+*/
+
+double
+inner(valarray<double> const &x, 
+      valarray<double> const &y) {
+    double total = 0;
+    for(unsigned i = 0; i < x.size(); i++)
+        total += x[i]*y[i];
+    return total;// (x*y).sum(); <- this is more concise, but ineff
+}
+
+double compute_cost(valarray<double> const &A, 
+        valarray<double> const &b,
+        valarray<double> const &x,
+        const unsigned n) {
+    // computes cost = 2 b x - x A x
+    double cost = 2. * inner(b,x);
+    valarray<double> Ax(n);
+    for (unsigned i=0; i<n; i++) {
+        Ax[i] = 0;
+        for (unsigned j=0; j<n; j++) {
+            Ax[i] += A[i*n+j]*x[j];
+        }
+    }
+    return cost - inner(x,Ax);
+}
+void 
+conjugate_gradient(valarray<double> const &A, 
+           valarray<double> &x, 
+           valarray<double> const &b, 
+           unsigned const n, double const tol,
+           unsigned const max_iterations) {
+    //printf("Conjugate Gradient...\n");
+    valarray<double> Ap(n), p(n), r(n);
+    matrix_times_vector(A,x,Ap);
+    r=b-Ap; 
+    double r_r = inner(r,r);
+    unsigned k = 0;
+    double tol_squared = tol*tol;
+#ifdef EXAMINE_COST
+    double previousCost=compute_cost(A,b,x,n),cost;
+#endif
+    while(k < max_iterations && r_r > tol_squared) {
+        k++;
+        double r_r_new = r_r;
+        if(k == 1)
+            p = r;
+        else {
+            r_r_new = inner(r,r);
+            if(r_r_new<tol_squared) break;
+            p = r + (r_r_new/r_r)*p;
+        }
+        matrix_times_vector(A, p, Ap);
+        double alpha_k = r_r_new / inner(p, Ap);
+        x += alpha_k*p;
+#ifdef EXAMINE_COST
+        cost=compute_cost(A,b,x,n);
+        printf("  CG[%d] %.15f %.15f\n",k,previousCost,cost);
+        previousCost=cost;
+#endif
+        r -= alpha_k*Ap;
+        r_r = r_r_new;
+    }
+    //printf("  CG finished after %d iterations\n",k);
+    //printf("njh: %d iters, Linfty = %g L2 = %g\n", k, 
+    //std::max(-r.min(), r.max()), sqrt(r_r));
+    // x is solution
+}
-- 
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