/// <summary>
/// Adds the specified sparse rows regarding defined multipliers.
/// </summary>
/// <param name="a1">The a1.</param>
/// <param name="a2">The a2.</param>
/// <param name="a1Coef">The a1 coef.</param>
/// <param name="a2Coef">The a2 coef.</param>
/// <returns> a1 * a1Coef + a2 * a2Coef</returns>
public static SparseRow Add(SparseRow a1, SparseRow a2, double a1Coef, double a2Coef)
{
var buf = new SparseRow(a2.Size + a1.Size);
//based on https://stackoverflow.com/a/12993675/1106889
//result = a1 * a1Coef + a2 * a2Coef;
var c1 = 0;
var c2 = 0;
var i1s = a1.Indexes;
var v1s = a1.Values;
var l1 = a1.Size;
var i2s = a2.Indexes;
var v2s = a2.Values;
var l2 = a2.Size;
while (c1 < l1 && c2 < l2)
{
var i1 = i1s[c1];
var i2 = i2s[c2];
var v1 = v1s[c1];
var v2 = v2s[c2];
if (i1 > i2)
{
buf.Add(i2 /*or i1*/, v2 * a2Coef);
c2++;
}
else if (i1 < i2)
{
buf.Add(i1, v1 * a1Coef);
c1++;
}
else
{//common
var newValue = v1 * a1Coef + v2 * a2Coef;
buf.Add(i1, newValue);
c1++;
c2++;
}
}
return(buf);
}
/// <summary>
/// Eliminates the specified index of <see cref="eliminated"/> row by adding appropriated multiply of <see cref="eliminator"/> to it.
/// </summary>
/// <param name="eliminator">The eliminator row.</param>
/// <param name="eliminated">The eliminated row.</param>
/// <param name="eliminateIndex">The index of eliminated member.</param>
/// <returns>Eliminated version of <see cref="eliminated"/></returns>
public static SparseRow Eliminate(SparseRow eliminator, SparseRow eliminated, int eliminateIndex, double epsilon = 0)
{
var buf = new SparseRow(eliminated.Size + eliminator.Size);
//based on https://stackoverflow.com/a/12993675/1106889
//result = eliminator * coef + eliminated
double coef;
{
var t1 = Array.BinarySearch(eliminator.Indexes, 0, eliminator.Size, eliminateIndex);
var t2 = Array.BinarySearch(eliminated.Indexes, 0, eliminated.Size, eliminateIndex);
if (t1 < 0 || t2 < 0)
{
throw new Exception();
}
coef = -eliminated.Values[t2] / eliminator.Values[t1];
}
var c1 = 0;
var c2 = 0;
var i1s = eliminator.Indexes;
var v1s = eliminator.Values;
var l1 = eliminator.Size;
var i2s = eliminated.Indexes;
var v2s = eliminated.Values;
var l2 = eliminated.Size;
while (c1 < l1 && c2 < l2)
{
var i1 = i1s[c1];
var i2 = i2s[c2];
var v1 = v1s[c1];
var v2 = v2s[c2];
if (i1 > i2)
{
buf.Add(i2 /*or i1*/, v2);
c2++;
}
else if (i1 < i2)
{
buf.Add(i1, v1 * coef);
c1++;
}
else
{//common
if (i1 != i2)
{
throw new Exception();
}
var newValue = v1 * coef + v2;
if (i1 == eliminateIndex || Math.Abs(newValue) < epsilon)
{
//this is eliminated item, newValue should be zero and nothing to add
if (Math.Abs(newValue) > 1e-6)
{
throw new Exception("wrong result");
}
}
else
{
buf.Add(i1, newValue);
}
c1++;
c2++;
}
}
//tail
{
for (; c1 < l1; c1++)
{
var i1 = i1s[c1];
var v1 = v1s[c1];
buf.Add(i1, v1 * coef);
}
for (; c2 < l2; c2++)
{
var i2 = i2s[c2];
var v2 = v2s[c2];
buf.Add(i2, v2);
}
}
return(buf);
}
