require_relative '../../spec_helper' describe "Math.gamma" do it "returns +infinity given 0" do Math.gamma(0).should == Float::INFINITY end platform_is_not :windows do # https://bugs.ruby-lang.org/issues/12249 it "returns -infinity given -0.0" do Math.gamma(-0.0).should == -Float::INFINITY end end it "returns Math.sqrt(Math::PI) given 0.5" do Math.gamma(0.5).should be_close(Math.sqrt(Math::PI), TOLERANCE) end # stop at n == 23 because 23! cannot be exactly represented by IEEE 754 double it "returns exactly (n-1)! given n for n between 2 and 23" do fact = 1 2.upto(23) do |n| fact *= (n - 1) Math.gamma(n).should == fact end end it "returns approximately (n-1)! given n for n between 24 and 30" do fact2 = 1124000727777607680000 # 22! 24.upto(30) do |n| fact2 *= n - 1 # compare only the first 12 places, tolerate the rest Math.gamma(n).should be_close(fact2, fact2.to_s[12..-1].to_i) end end it "returns good numerical approximation for gamma(3.2)" do Math.gamma(3.2).should be_close(2.423965, TOLERANCE) end it "returns good numerical approximation for gamma(-2.15)" do Math.gamma(-2.15).should be_close(-2.999619, TOLERANCE) end it "returns good numerical approximation for gamma(0.00001)" do Math.gamma(0.00001).should be_close(99999.422794, TOLERANCE) end it "returns good numerical approximation for gamma(-0.00001)" do Math.gamma(-0.00001).should be_close(-100000.577225, TOLERANCE) end it "raises Math::DomainError given -1" do lambda { Math.gamma(-1) }.should raise_error(Math::DomainError) end # See https://bugs.ruby-lang.org/issues/10642 it "returns +infinity given +infinity" do Math.gamma(infinity_value).infinite?.should == 1 end it "raises Math::DomainError given negative infinity" do lambda { Math.gamma(-Float::INFINITY) }.should raise_error(Math::DomainError) end it "returns NaN given NaN" do Math.gamma(nan_value).nan?.should be_true end end