Inverses for •math.Fact and •math.LogFact

This commit is contained in:
Marshall Lochbaum 2022-11-26 14:17:27 -05:00
parent a3df482acd
commit d911eafd31

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@ -90,6 +90,18 @@ GC1f(root, sqrt(xv), "√: Getting square root of non-number")
f64 fact(f64 x) { return tgamma(x+1); }
f64 logfact(f64 x) { return lgamma(x+1); }
NOINLINE f64 logfact_inv(f64 y) {
if (!(y >= -0.12)) thrM("⁼: required factorial result too small");
if (y == INFINITY) return y;
f64 x = 4;
PLAINLOOP for (usz i = 0; i < 20; i++) {
f64 x0 = x;
x += (y - logfact(x)) / log(0.52 + x);
if (x == x0) break;
}
return x;
}
f64 fact_inv(f64 y) { return logfact_inv(log(y)); }
#define P1(N) { if(isArr(x)) { SLOW1("arithm " #N, x); return arith_recm(N##_c1, x); } }
B pow_c1(B t, B x) { if (isF64(x)) return m_f64( exp(x.f)); P1( pow); thrM("⋆: Getting exp of non-number"); }
@ -102,7 +114,7 @@ static NOINLINE B arith_recm_slow(f64 (*fn)(f64), BB2B rec, B x, char* s) {
}
#define MATH(n,N) B n##_c1(B t, B x) { return arith_recm_slow(n, n##_c1, x, #N); }
MATH(cbrt,Cbrt) MATH(log2,Log2) MATH(log10,Log10) MATH(log1p,Log1p) MATH(expm1,Expm1)
MATH(fact,Fact) MATH(logfact,LogFact) MATH(erf,Erf) MATH(erfc,ErfC)
MATH(fact,Fact) MATH(logfact,LogFact) MATH(logfact_inv,LogFact) MATH(fact_inv,Fact) MATH(erf,Erf) MATH(erfc,ErfC)
#define TRIG(n,N) MATH(n,N) MATH(a##n,A##n) MATH(n##h,N##h) MATH(a##n##h,A##n##h)
TRIG(sin,Sin) TRIG(cos,Cos) TRIG(tan,Tan)
#undef TRIG
@ -142,5 +154,7 @@ void arith_init() {
INVERSE_PAIR(cosh, acosh)
INVERSE_PAIR(tanh, atanh)
INVERSE_PAIR(expm1, log1p)
c(BFn,bi_fact)->im = fact_inv_c1;
c(BFn,bi_logfact)->im = logfact_inv_c1;
#undef INVERSE_PAIR
}