class Matrix

As a matter of fact, current version of the Matrix class (by Marc-Andre Lafortune) does not work with physical magnitudes. It is a feature of the physical magnitudes, that they do not allow themselves summed with plain numbers or incompatible magnitudes. But current version of Matrix class, upon matrix multiplication, performs needless addition of the matrix elements to literal numeric 0.

The obvious solution is to patch Matrix class so that the needless addition to literal 0 is no longer performed.

More systematically, abstract algebra is to be added to Ruby, and Matrix is to require that its elements comply with monoid, group, ring, field, depending on the operation one wants to do with such matrices.

Public Class Methods

wildcard_zero(r_count, c_count=r_count) click to toggle source

Creates a matrix of prescribed dimensions filled with wildcard zeros.

# File lib/sy/matrix.rb, line 91
def Matrix.wildcard_zero r_count, c_count=r_count
  build r_count, c_count do |r, c| WILDCARD_ZERO end
end

Public Instance Methods

*(arg) click to toggle source

Matrix multiplication.

# File lib/sy/matrix.rb, line 31
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?
    return map { |e| e * arg }
  else
    compat_1, compat_2 = arg.coerce self
    return compat_1 * compat_2
  end
end

/(other) click to toggle source

Matrix division (multiplication by the inverse).

Matrix[[7,6], [3,9]] / Matrix[[2,9], [3,1]]
  => -7  1
     -3 -6

# File lib/sy/matrix.rb, line 74
def /(other)
  case other
  when Numeric
    rows = @rows.collect do |row| row.collect {|e| e / other } end
    return new_matrix rows, column_count
  when Matrix
    return self * other.inverse
  when SY::Magnitude # newly added - multiplication by a magnitude
    return self * ( 1 / other )
  else
    return apply_through_coercion(other, __method__)
  end
end