// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
// SPDX-License-Identifier: MIT

package linalg

import (
	"math"
	"testing"
)

// TestDetFactorsThroughParallelDispatch drives base.Factor's rank-1
// update dispatch through the public Det entry: a 200 by 200 upper
// triangular matrix keeps every pivot on the diagonal, and the first
// pivot's update spans 199 rows times 200 columns, past the dispatch
// quantum, so the crewed path runs rather than the inline one. No row
// changes under the elimination, since the multiplier of every row is
// zero, so the determinant is exactly 2 to the 200th, which float64
// holds as an exact power of two.
func TestDetFactorsThroughParallelDispatch(t *testing.T) {
	const n = 200
	vals := make([]float64, n*n)
	for i := range n {
		for j := i; j < n; j++ {
			vals[i*n+j] = 2
		}
	}
	d, err := Det(mustFloats(t, vals, n, n))
	if err != nil {
		t.Fatalf("Det: %v", err)
	}
	if want := math.Ldexp(1, 200); d != want {
		t.Fatalf("Det = %v, want exactly %v", d, want)
	}
}