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Diffstat (limited to 'spec/ruby/core/math/gamma_spec.rb')
-rw-r--r-- | spec/ruby/core/math/gamma_spec.rb | 69 |
1 files changed, 69 insertions, 0 deletions
diff --git a/spec/ruby/core/math/gamma_spec.rb b/spec/ruby/core/math/gamma_spec.rb new file mode 100644 index 0000000000..eb26f25bfe --- /dev/null +++ b/spec/ruby/core/math/gamma_spec.rb @@ -0,0 +1,69 @@ +require File.expand_path('../../../spec_helper', __FILE__) + +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 |