Method: Matrix#*

Defined in:
lib/y_support/abstract_algebra.rb

#*(arg) ⇒ Object

Matrix multiplication.



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# File 'lib/y_support/abstract_algebra.rb', line 185

def * arg # arg is matrix or vector or number
  case arg
  when Numeric
    rows = @rows.map { |row| row.map { |e| e * arg } }
    return new_matrix rows, column_size
  when Vector
    arg = Matrix.column_vector arg
    result = self * arg
    return result.column 0
  when Matrix
    Matrix.Raise ErrDimensionMismatch if column_size != arg.row_size
    if empty? then # if empty?, then reduce uses WILDCARD_ZERO
      rows = Array.new row_size do |i|
        Array.new arg.column_size do |j|
          ( 0...column_size ).reduce WILDCARD_ZERO do |sum, c|
            sum + arg[c, j] * self[i, c]
          end
        end
      end
    else             # if non-empty, reduce proceeds without WILDCARD_ZERO
      rows = Array.new row_size do |i|
        Array.new arg.column_size do |j|
          ( 0...column_size ).map { |c| arg[c, j] * self[i, c] }.reduce :+
        end
      end
    end
    return new_matrix( rows, arg.column_size )
  when SY::Magnitude # newly added - multiplication by a magnitude
    # I am not happy with this explicit switch on SY::Magnitude type here.
    # Perhaps coerce should handle this?
    rows = Array.new row_size do |i|
      Array.new column_size do |j|
        self[i, j] * arg
      end
    end
    return self.class[ *rows ]
  else
    compat_1, compat_2 = arg.coerce self
    return compat_1 * compat_2
  end
end