private void sprsax(VecDoub sa, VecLong ija, VecDoub x, VecDoub b, int n)
{
if (ija[1] != n + 2)
{
new Exception("sprsax: mismatched vector and matrix");
}
int i;
long k;
for (i = 0; i < n; i++)
{
b[i] = sa[i] * x[i]; //Diagonal entries
for (k = ija[i]; k <= ija[i + 1] - 1; k++) //TODO: Verify this.
{
b[i] += sa[(int)k] * x[(int)ija[(int)k]]; //Off diagonal entries. Multiply the entry of the matrix by the x of the corresponding column.
}
//TODO: Find out how to reference arrays in C# with some thing that could be > 2 billion (max value of integer).
}
}
private void sprstx(VecDoub sa, VecLong ija, VecDoub x, VecDoub b, int n)
{
int i, j;
long k;
if (ija[1] != n + 2)
{
new Exception("mismatched vector and matrix in sprstx");
}
for (i = 0; i < n; i++)
{
b[i] = sa[i] * x[i]; //First come the diagonal terms
}
for (i = 0; i < n; i++)
{//Now loop over the off diagonal terms.
for (k = ija[i]; k <= ija[i + 1] - 1; k++)
{
j = (int)ija[(int)k];
b[j] += sa[(int)k] * x[i]; //Because this is multiplication by the transpose, the indices of b and x interchange.
}
}
}
public Sprsin(MatDoub a)//TODO: make a VecULong type to further save on space.
{
/************************************
* Converts a square matrix a[1..n][1..n] into row-indexed sparse storage mode.
* Only elements of a with magnitude ≥thresh are retained. Output is in two linear arrays
* with dimension nmax (an input parameter): sa[1..] contains array values, indexed by ija[1..].
* The number of elements filled of sa and ija on output are both ija[ija[1]-1]-1
************************************/
sa = new VecDoub(new double[nmax]);
ija = new VecLong(18, new long[nmax], 0);
n = a.nrows();
int i, j, k;
for (j = 0; j < n; j++)
{
sa[j] = a[j][j]; //Store the diagonal elements.
}
ija[0] = n + 1; //Index to the first off diagonal element if any.
k = n;
for (i = 0; i < n; i++)
{
for (j = 0; j < n; j++)
{
if (Math.Abs(a[i][j]) >= thresh && i != j)
{
if (++k > (int)nmax)
{
throw new Exception("sprsin: nmax too small");
}
sa[k] = a[i][j]; //Store off diagonal elements.
ija[k] = j; //And their column indices.
}
}
ija[i + 1] = k + 1; //As each row is completed, store index to next
}
this.numelements = k + 1;
}
