Reverse lookup

Recover candidate birth dates from four BaZi pillars or from chart features. All computation runs in the wasm core (pruned enumeration + full re-charting, zero divergence from forward charting); the Go side is a typed wrapper. Concepts, how pillars follow the Config boundaries, and the multi-solution / truncation semantics are on the reverse lookup guide.

cands, err := iztro.SolarDatesByBazi(
    iztro.Pillar{iztro.StemGeng, iztro.BranchChen},
    iztro.Pillar{iztro.StemJia, iztro.BranchShen},
    iztro.Pillar{iztro.StemBing, iztro.BranchWu},
    iztro.Pillar{iztro.StemGeng, iztro.BranchYin},
    1900, 2100, nil)

Stems, branches, classes and stars all take language-independent keys (the StemGeng, BranchChen, ClassWood3rd, StarZiweiMaj constants and family). Both entry points have Context variants; ctx cancels the wait for a wasm instance.

Types

Pillar

type Pillar [2]string

One pillar: [stem key, branch key]. The RawDates.ChineseDate.YearlyKeys family on an astrolabe converts directly: iztro.Pillar(cd.YearlyKeys).

BirthCandidate

One candidate birth moment, ready to hand to BySolar.

StarPosition

A star and the branch of the palace it sits in: the atomic condition of a feature lookup.

ReverseCriteria

The condition set of a feature lookup. Zero values mean "not stated": an empty string leaves that condition unset, a zero YearRange takes [1900, 2100], a Limit of 0 takes the core default (512), and a nil FixLeap takes the core default true (it is a *bool; switch it off explicitly with iztro.Bool(false)). Every condition is optional, but at least one must be given.

ReverseResult

SolarDatesByBazi

Recover solar birth dates from four BaZi pillars.

func SolarDatesByBazi(yearly, monthly, daily, hourly Pillar,
    startYear, endYear int, config *Config) ([]BirthCandidate, error)

func SolarDatesByBaziContext(ctx context.Context, yearly, monthly, daily, hourly Pillar,
    startYear, endYear int, config *Config) ([]BirthCandidate, error)

The pillars are interpreted under the boundary readings of config (YearDivide for the year pillar, HoroscopeDivide for the month pillar, DayDivide for the late Zi hour) — the same semantics as the RawDates.ChineseDate a charted astrolabe reports, so reversing any chart's pillars always includes that chart's birth moment. A set of pillars recurs roughly every 60 years within the range; an hour branch of Zi may yield two candidates on adjacent days because of the early/late Zi hour split.

Example

a, _ := iztro.BySolar("2000-8-16", 2, iztro.GenderFemale, true, iztro.LanguageEnUS, nil)
cd := a.RawDates.ChineseDate

cands, err := iztro.SolarDatesByBazi(
    iztro.Pillar(cd.YearlyKeys), iztro.Pillar(cd.MonthlyKeys),
    iztro.Pillar(cd.DailyKeys), iztro.Pillar(cd.HourlyKeys),
    1900, 2100, nil)
if err != nil {
    log.Fatal(err)
}
for _, c := range cands {
    fmt.Println(c.SolarDate, c.TimeIndex)
}

Output

1940-8-31 2
2000-8-16 2
2060-8-1 2

Errors A pillar with mismatched stem/branch polarity (such as 甲丑 Jia-Chou — a yang stem on a yin branch), or a year range that is reversed or outside 1583–9999, returns an ErrInvalidArgument-class error (matchable with errors.Is). See Error handling.

ReverseChart

Recover candidate birth dates from chart features.

func ReverseChart(criteria *ReverseCriteria, config *Config) (*ReverseResult, error)

func ReverseChartContext(ctx context.Context, criteria *ReverseCriteria,
    config *Config) (*ReverseResult, error)

Judgement runs entirely under config: the mutagen table, the school and every boundary follow it, so charting a candidate with the same config is guaranteed to satisfy every condition. Chart layout does not depend on gender (gender only affects the direction the decadal horoscope advances), so the criteria carry no gender.

Example

r, err := iztro.ReverseChart(&iztro.ReverseCriteria{
    SoulBranch:        iztro.BranchWu,
    FiveElementsClass: iztro.ClassWood3rd,
    Stars:             []iztro.StarPosition{{Star: iztro.StarZiweiMaj, Branch: iztro.BranchWu}},
    Mutagens:          [4]string{iztro.StarTaiyangMaj, "", "", ""},
    YearRange:         [2]int{1998, 2002},
}, nil)
if err != nil {
    log.Fatal(err)
}
fmt.Println(len(r.Candidates), r.Truncated)

Output

39 false

Errors A nil criteria, empty criteria, a horoscope-scope flow star in Stars, or an invalid year range returns an ErrInvalidArgument-class error.