/*
* Compute
* X = B*diag(D).-1 flags & RIGHT == true
* X = diag(D).-1*C flags & LEFT == true
*
* Arguments:
* B M-by-N matrix if flags&RIGHT == true or N-by-M matrix if flags&LEFT == true
*
* D N element column or row vector or N-by-N matrix
*
* flags Indicator bits, LEFT or RIGHT
*/
func SolveDiag(B, D *matrix.FloatMatrix, flags Flags) {
var c, d0 matrix.FloatMatrix
if D.Cols() == 1 {
// diagonal is column vector
switch flags & (LEFT | RIGHT) {
case LEFT:
// scale rows; for each column element-wise multiply with D-vector
for k := 0; k < B.Cols(); k++ {
B.SubMatrix(&c, 0, k, B.Rows(), 1)
c.Div(D)
}
case RIGHT:
// scale columns
for k := 0; k < B.Cols(); k++ {
B.SubMatrix(&c, 0, k, B.Rows(), 1)
// scale the column
c.Scale(1.0 / D.GetAt(k, 0))
}
}
} else {
var d *matrix.FloatMatrix
if D.Rows() == 1 {
d = D
} else {
D.SubMatrix(&d0, 0, 0, 1, D.Cols(), D.LeadingIndex()+1)
d = &d0
}
switch flags & (LEFT | RIGHT) {
case LEFT:
for k := 0; k < B.Rows(); k++ {
B.SubMatrix(&c, k, 0, 1, B.Cols())
// scale the row
c.Scale(1.0 / d.GetAt(0, k))
}
case RIGHT:
// scale columns
for k := 0; k < B.Cols(); k++ {
B.SubMatrix(&c, 0, k, B.Rows(), 1)
// scale the column
c.Scale(1.0 / d.GetAt(0, k))
}
}
}
}
