Implementation
void dtftri(
final String TRANSR,
final String UPLO,
final String DIAG,
final int N,
final Array<double> A_,
final Box<int> INFO,
) {
final A = A_.having(offset: zeroIndexedArrayOffset);
const ONE = 1.0;
bool LOWER, NISODD, NORMALTRANSR;
int N1, N2, K = 0;
// Test the input parameters.
INFO.value = 0;
NORMALTRANSR = lsame(TRANSR, 'N');
LOWER = lsame(UPLO, 'L');
if (!NORMALTRANSR && !lsame(TRANSR, 'T')) {
INFO.value = -1;
} else if (!LOWER && !lsame(UPLO, 'U')) {
INFO.value = -2;
} else if (!lsame(DIAG, 'N') && !lsame(DIAG, 'U')) {
INFO.value = -3;
} else if (N < 0) {
INFO.value = -4;
}
if (INFO.value != 0) {
xerbla('DTFTRI', -INFO.value);
return;
}
// Quick return if possible
if (N == 0) return;
// If N is odd, set NISODD = true;
// If N is even, set K = N/2 and NISODD = false;
if ((N % 2) == 0) {
K = N ~/ 2;
NISODD = false;
} else {
NISODD = true;
}
// Set N1 and N2 depending on LOWER
if (LOWER) {
N2 = N ~/ 2;
N1 = N - N2;
} else {
N1 = N ~/ 2;
N2 = N - N1;
}
// start execution: there are eight cases
if (NISODD) {
// N is odd
if (NORMALTRANSR) {
// N is odd and TRANSR = 'N'
if (LOWER) {
// SRPA for LOWER, NORMAL and N is odd ( a(0:n-1,0:n1-1) )
// T1 -> a(0,0), T2 -> a(0,1), S -> a(n1,0)
// T1 -> a(0), T2 -> a(n), S -> a(n1)
dtrtri('L', DIAG, N1, A(0).asMatrix(N), N, INFO);
if (INFO.value > 0) return;
dtrmm('R', 'L', 'N', DIAG, N2, N1, -ONE, A(0).asMatrix(N), N,
A(N1).asMatrix(N), N);
dtrtri('U', DIAG, N2, A(N).asMatrix(N), N, INFO);
if (INFO.value > 0) INFO.value += N1;
if (INFO.value > 0) return;
dtrmm('L', 'U', 'T', DIAG, N2, N1, ONE, A(N).asMatrix(N), N,
A(N1).asMatrix(N), N);
} else {
// SRPA for UPPER, NORMAL and N is odd ( a(0:n-1,0:n2-1)
// T1 -> a(n1+1,0), T2 -> a(n1,0), S -> a(0,0)
// T1 -> a(n2), T2 -> a(n1), S -> a(0)
dtrtri('L', DIAG, N1, A(N2).asMatrix(N), N, INFO);
if (INFO.value > 0) return;
dtrmm('L', 'L', 'T', DIAG, N1, N2, -ONE, A(N2).asMatrix(N), N,
A(0).asMatrix(N), N);
dtrtri('U', DIAG, N2, A(N1).asMatrix(N), N, INFO);
if (INFO.value > 0) INFO.value += N1;
if (INFO.value > 0) return;
dtrmm('R', 'U', 'N', DIAG, N1, N2, ONE, A(N1).asMatrix(N), N,
A(0).asMatrix(N), N);
}
} else {
// N is odd and TRANSR = 'T'
if (LOWER) {
// SRPA for LOWER, TRANSPOSE and N is odd
// T1 -> a(0), T2 -> a(1), S -> a(0+n1*n1)
dtrtri('U', DIAG, N1, A(0).asMatrix(N1), N1, INFO);
if (INFO.value > 0) return;
dtrmm('L', 'U', 'N', DIAG, N1, N2, -ONE, A(0).asMatrix(N1), N1,
A(N1 * N1).asMatrix(N1), N1);
dtrtri('L', DIAG, N2, A(1).asMatrix(N1), N1, INFO);
if (INFO.value > 0) INFO.value += N1;
if (INFO.value > 0) return;
dtrmm('R', 'L', 'T', DIAG, N1, N2, ONE, A(1).asMatrix(N1), N1,
A(N1 * N1).asMatrix(N1), N1);
} else {
// SRPA for UPPER, TRANSPOSE and N is odd
// T1 -> a(0+n2*n2), T2 -> a(0+n1*n2), S -> a(0)
dtrtri('U', DIAG, N1, A(N2 * N2).asMatrix(N2), N2, INFO);
if (INFO.value > 0) return;
dtrmm('R', 'U', 'T', DIAG, N2, N1, -ONE, A(N2 * N2).asMatrix(N2), N2,
A(0).asMatrix(N2), N2);
dtrtri('L', DIAG, N2, A(N1 * N2).asMatrix(N2), N2, INFO);
if (INFO.value > 0) INFO.value += N1;
if (INFO.value > 0) return;
dtrmm('L', 'L', 'N', DIAG, N2, N1, ONE, A(N1 * N2).asMatrix(N2), N2,
A(0).asMatrix(N2), N2);
}
}
} else {
// N is even
if (NORMALTRANSR) {
// N is even and TRANSR = 'N'
if (LOWER) {
// SRPA for LOWER, NORMAL, and N is even ( a(0:n,0:k-1) )
// T1 -> a(1,0), T2 -> a(0,0), S -> a(k+1,0)
// T1 -> a(1), T2 -> a(0), S -> a(k+1)
dtrtri('L', DIAG, K, A(1).asMatrix(N + 1), N + 1, INFO);
if (INFO.value > 0) return;
dtrmm('R', 'L', 'N', DIAG, K, K, -ONE, A(1).asMatrix(N + 1), N + 1,
A(K + 1).asMatrix(N + 1), N + 1);
dtrtri('U', DIAG, K, A(0).asMatrix(N + 1), N + 1, INFO);
if (INFO.value > 0) INFO.value += K;
if (INFO.value > 0) return;
dtrmm('L', 'U', 'T', DIAG, K, K, ONE, A(0).asMatrix(N + 1), N + 1,
A(K + 1).asMatrix(N + 1), N + 1);
} else {
// SRPA for UPPER, NORMAL, and N is even ( a(0:n,0:k-1) )
// T1 -> a(k+1,0) , T2 -> a(k,0), S -> a(0,0)
// T1 -> a(k+1), T2 -> a(k), S -> a(0)
dtrtri('L', DIAG, K, A(K + 1).asMatrix(N + 1), N + 1, INFO);
if (INFO.value > 0) return;
dtrmm('L', 'L', 'T', DIAG, K, K, -ONE, A(K + 1).asMatrix(N + 1), N + 1,
A(0).asMatrix(N + 1), N + 1);
dtrtri('U', DIAG, K, A(K).asMatrix(N + 1), N + 1, INFO);
if (INFO.value > 0) INFO.value += K;
if (INFO.value > 0) return;
dtrmm('R', 'U', 'N', DIAG, K, K, ONE, A(K).asMatrix(N + 1), N + 1,
A(0).asMatrix(N + 1), N + 1);
}
} else {
// N is even and TRANSR = 'T'
if (LOWER) {
// SRPA for LOWER, TRANSPOSE and N is even (see paper)
// T1 -> B(0,1), T2 -> B(0,0), S -> B(0,k+1)
// T1 -> a(0+k), T2 -> a(0+0), S -> a(0+k*(k+1)); lda=k
dtrtri('U', DIAG, K, A(K).asMatrix(K), K, INFO);
if (INFO.value > 0) return;
dtrmm('L', 'U', 'N', DIAG, K, K, -ONE, A(K).asMatrix(K), K,
A(K * (K + 1)).asMatrix(K), K);
dtrtri('L', DIAG, K, A(0).asMatrix(K), K, INFO);
if (INFO.value > 0) INFO.value += K;
if (INFO.value > 0) return;
dtrmm('R', 'L', 'T', DIAG, K, K, ONE, A(0).asMatrix(K), K,
A(K * (K + 1)).asMatrix(K), K);
} else {
// SRPA for UPPER, TRANSPOSE and N is even (see paper)
// T1 -> B(0,k+1), T2 -> B(0,k), S -> B(0,0)
// T1 -> a(0+k*(k+1)), T2 -> a(0+k*k), S -> a(0+0)); lda=k
dtrtri('U', DIAG, K, A(K * (K + 1)).asMatrix(K), K, INFO);
if (INFO.value > 0) return;
dtrmm('R', 'U', 'T', DIAG, K, K, -ONE, A(K * (K + 1)).asMatrix(K), K,
A(0).asMatrix(K), K);
dtrtri('L', DIAG, K, A(K * K).asMatrix(K), K, INFO);
if (INFO.value > 0) INFO.value += K;
if (INFO.value > 0) return;
dtrmm('L', 'L', 'N', DIAG, K, K, ONE, A(K * K).asMatrix(K), K,
A(0).asMatrix(K), K);
}
}
}
}
