Golang Float.Abs方法代码示例

// BigCommaf produces a string form of the given big.Float in base 10
// with commas after every three orders of magnitude.
func BigCommaf(v *big.Float) string {
	buf := &bytes.Buffer{}
	if v.Sign() < 0 {
		buf.Write([]byte{'-'})
		v.Abs(v)
	}

	comma := []byte{','}

	parts := strings.Split(v.Text('f', -1), ".")
	pos := 0
	if len(parts[0])%3 != 0 {
		pos += len(parts[0]) % 3
		buf.WriteString(parts[0][:pos])
		buf.Write(comma)
	}
	for ; pos < len(parts[0]); pos += 3 {
		buf.WriteString(parts[0][pos : pos+3])
		buf.Write(comma)
	}
	buf.Truncate(buf.Len() - 1)

	if len(parts) > 1 {
		buf.Write([]byte{'.'})
		buf.WriteString(parts[1])
	}
	return buf.String()
}

func TestPow(t *testing.T) {
	x := big.NewFloat(0.12381245613960218386)
	n := 3
	res := Pow(x, n)
	exp := big.NewFloat(0.00189798605)
	diff := new(big.Float).Sub(res, exp)
	diff = diff.Abs(diff)
	if diff.Cmp(big.NewFloat(0.00000001)) >= 0 {
		log.Fatal("Pow failed:", exp, res)
	}
}

func TestRoot(t *testing.T) {
	x := big.NewFloat(0.12381245613960218386)
	n := 16
	res := Root(x, n)
	exp := big.NewFloat(0.8776023372475015)
	diff := new(big.Float).Sub(res, exp)
	diff = diff.Abs(diff)
	if diff.Cmp(big.NewFloat(0.00000001)) >= 0 {
		log.Fatal("Exp failed:", exp, res)
	}
}

// hypot for big.Float
func hypot(p, q *big.Float) *big.Float {
	// special cases
	switch {
	case p.IsInf() || q.IsInf():
		return big.NewFloat(math.Inf(1))
	}
	p = p.Abs(p)
	q = q.Abs(q)
	if p.Cmp(p) < 0 {
		p, q = q, p
	}
	if p.Cmp(big.NewFloat(0)) == 0 {
		return big.NewFloat(0)
	}
	q = q.Quo(q, p)
	return sqrt(q.Mul(q, q).Add(q, big.NewFloat(1))).Mul(q, p)
}

// Given a vector of real numbers x = [x_0, x_1, ..., x_n], this
// uses the PSLQ algorithm to find a list of integers
// [c_0, c_1, ..., c_n] such that
//
//     |c_1 * x_1 + c_2 * x_2 + ... + c_n * x_n| < tolerance
//
// and such that max |c_k| < maxcoeff. If no such vector exists, Pslq
// returns one of the errors in this package depending on whether it
// has run out of iterations, precision or explored up to the
// maxcoeff. The tolerance defaults to 3/4 of the precision.
//
// This is a fairly direct translation of the pseudocode given by
// David Bailey, "The PSLQ Integer Relation Algorithm":
// http://www.cecm.sfu.ca/organics/papers/bailey/paper/html/node3.html
//
// If a result is returned, the first non-zero element will be positive
func (e *Pslq) Run(x []big.Float) ([]big.Int, error) {
	n := len(x)
	if n <= 1 {
		return nil, ErrorBadArguments
	}

	// At too low precision, the algorithm becomes meaningless
	if e.prec < 64 {
		return nil, ErrorPrecisionTooLow
	}

	if e.verbose && int(e.prec)/max(2, int(n)) < 5 {
		log.Printf("Warning: precision for PSLQ may be too low")
	}

	if e.verbose {
		log.Printf("PSLQ using prec %d and tol %g", e.prec, e.tol)
	}

	if e.tol.Sign() == 0 {
		return nil, ErrorToleranceRoundsToZero
	}

	// Temporary variables
	tmp0 := new(big.Float).SetPrec(e.prec)
	tmp1 := new(big.Float).SetPrec(e.prec)
	bigTmp := new(big.Int)

	// Convert to use 1-based indexing to allow us to be
	// consistent with Bailey's indexing.
	xNew := make([]big.Float, len(x)+1)
	minx := new(big.Float).SetPrec(e.prec)
	minxFirst := true
	for i, xk := range x {
		p := &xNew[i+1]
		p.Set(&xk)
		tmp0.Abs(p)
		if minxFirst || tmp0.Cmp(minx) < 0 {
			minxFirst = false
			minx.Set(tmp0)
		}
	}
	x = xNew
	if debug {
		printVector("x", x)
	}

	// Sanity check on magnitudes
	if minx.Sign() == 0 {
		return nil, ErrorZeroArguments
	}
	tmp1.SetInt64(128)
	tmp0.Quo(&e.tol, tmp1)
	if minx.Cmp(tmp0) < 0 { //  minx < tol/128
		return nil, ErrorArgumentTooSmall
	}

	tmp0.SetInt64(4)
	tmp1.SetInt64(3)
	tmp0.Quo(tmp0, tmp1)
	var γ big.Float
	e.Sqrt(tmp0, &γ) // sqrt(4<<prec)/3)
	if debug {
		fmt.Printf("γ = %f\n", &γ)
	}
	A := newBigIntMatrix(n+1, n+1)
	B := newBigIntMatrix(n+1, n+1)
	H := newMatrix(n+1, n+1)
	// Initialization Step 1
	//
	// Set the n×n matrices A and B to the identity.
	for i := 1; i <= n; i++ {
		for j := 1; j <= n; j++ {
			if i == j {
				A[i][j].SetInt64(1)
				B[i][j].SetInt64(1)
			} else {
				A[i][j].SetInt64(0)
				B[i][j].SetInt64(0)
			}
			H[i][j].SetInt64(0)
		}
	}
	if debug {
//.........这里部分代码省略.........

func arithAbs(a *big.Float) (*big.Float, error) {
	return a.Abs(a), nil
}