public void TestSpecialFunctions_Digamma()
{
// ensure poles return NaN
Assert.That(Fn.Digamma(0.0), Is.NaN, "A1");
Assert.That(Fn.Digamma(-1.0), Is.NaN, "A2");
Assert.That(Fn.Digamma(-2.0), Is.NaN, "A3");
Assert.That(Fn.Digamma(-20.0), Is.NaN, "A4");
Assert.That(Fn.Digamma(-20.0000000001), Is.Not.NaN, "A4b");
// Compare Gamma with Maple: "evalf(Psi(x),20);"
Assert.That(Fn.Digamma(0.001), NumericIs.AlmostEqualTo(-1000.5755719318103005), "B1");
Assert.That(Fn.Digamma(0.01), NumericIs.AlmostEqualTo(-100.56088545786867450), "B2");
Assert.That(Fn.Digamma(0.1), NumericIs.AlmostEqualTo(-10.423754940411076795), "B3");
Assert.That(Fn.Digamma(0.2), NumericIs.AlmostEqualTo(-5.2890398965921882955), "B4");
Assert.That(Fn.Digamma(0.4), NumericIs.AlmostEqualTo(-2.5613845445851161457), "B5");
Assert.That(Fn.Digamma(0.6), NumericIs.AlmostEqualTo(-1.5406192138931904148), "B6");
Assert.That(Fn.Digamma(0.9), NumericIs.AlmostEqualTo(-.75492694994705139189), "B7");
Assert.That(Fn.Digamma(0.999), NumericIs.AlmostEqualTo(-.57886180210864542646), "B8");
Assert.That(Fn.Digamma(1.0), NumericIs.AlmostEqualTo(-.57721566490153286061), "B9");
Assert.That(Fn.Digamma(1.001), NumericIs.AlmostEqualTo(-.57557193181030047147, 1e-14), "B10");
Assert.That(Fn.Digamma(1.5), NumericIs.AlmostEqualTo(.36489973978576520559e-1, 1e-14), "B11");
Assert.That(Fn.Digamma(1.9), NumericIs.AlmostEqualTo(.35618416116405971922), "B12");
Assert.That(Fn.Digamma(2.0), NumericIs.AlmostEqualTo(.42278433509846713939), "B13");
Assert.That(Fn.Digamma(10.0), NumericIs.AlmostEqualTo(2.2517525890667211076), "B14");
Assert.That(Fn.Digamma(10.51), NumericIs.AlmostEqualTo(2.3039997054324985520), "B15");
Assert.That(Fn.Digamma(100), NumericIs.AlmostEqualTo(4.6001618527380874002), "B16");
Assert.That(Fn.Digamma(-0.01), NumericIs.AlmostEqualTo(99.406213695944404856), "B17");
Assert.That(Fn.Digamma(-0.1), NumericIs.AlmostEqualTo(9.2450730500529486081), "B18");
Assert.That(Fn.Digamma(-0.5), NumericIs.AlmostEqualTo(.36489973978576520559e-1, 1e-14), "B19");
Assert.That(Fn.Digamma(-1.2), NumericIs.AlmostEqualTo(4.8683247666271948739), "B20");
Assert.That(Fn.Digamma(-2.01), NumericIs.AlmostEqualTo(100.89382514365634023, 1e-13), "B21");
Assert.That(Fn.Digamma(-100.01), NumericIs.AlmostEqualTo(104.57736050326787844, 1e-12), "B22");
}
