ruby--ruby/spec/ruby/library/matrix/exponent_spec.rb

require_relative '../../spec_helper'

ruby_version_is ""..."3.1" do
  require_relative 'fixtures/classes'
  require 'matrix'

  describe "Matrix#**" do

    describe "given an integer _n_" do
      it "multiples the Matrix by itself _n_ times" do
        m = Matrix[ [7,6], [3,9] ]
        (m ** 1).should == m
        (m ** 2).should == Matrix[ [67, 96], [48,99] ]
        (m ** 2).should == m * m
        (m ** 3).should == m * m * m
        (m ** 4).should == m * m * m * m
        (m ** 5).should == m * m * m * m * m
      end

      it "raises a ErrDimensionMismatch for non square matrices" do
        m = Matrix[ [1, 1], [1, 2], [2, 3]]
        -> { m ** 3 }.should raise_error(Matrix::ErrDimensionMismatch)
        -> { m ** 0 }.should raise_error(Matrix::ErrDimensionMismatch)
      end

      describe "that is < 0" do
        it "returns the inverse of **(-n)" do
          m = Matrix[ [1, 1], [1, 2] ]
          (m ** -2).should == Matrix[ [5, -3], [-3, 2]]
          (m ** -4).should == (m.inverse ** 4)
        end

        it "raises a ErrNotRegular for irregular matrices" do
          m = Matrix[ [1, 1], [1, 1] ]
          -> { m ** -2 }.should raise_error(Matrix::ErrNotRegular)
        end
      end

      ruby_version_is '3.1.0' do # https://bugs.ruby-lang.org/issues/17521
        describe "that is 0" do
          it "returns the identity for square matrices" do
            m = Matrix[ [1, 1], [1, 1] ]
            (m ** 0).should == Matrix.identity(2)
          end

          it "raises an ErrDimensionMismatch for non-square matrices" do
            m = Matrix[ [1, 1] ]
            -> { m ** 0 }.should raise_error(Matrix::ErrDimensionMismatch)
          end
        end
      end
    end

    it "returns the power for non integer powers" do
      a = Matrix[[5, 4], [4, 5]]
      ((a ** 0.5) ** 2).round(8).should == a
      a = Matrix[[7, 10], [15, 22]]
      ((a ** 0.25) ** 4).round(8).should == a
    end

    describe "for a subclass of Matrix" do
      it "returns an instance of that subclass" do
        (MatrixSub.ins ** 1).should be_an_instance_of(MatrixSub)
      end
    end
  end
end