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Singular and Non-singular Matrix

                                    Yuji Oyamada

                                 1 HVRL,   Keio University
2 Chair   for Computer Aided Medical Procedure (CAMP), Technische Universit:t M:nchen
                                                                           a   u


                                   April 10, 2012
Non-Singular




A is non-singular means that A is invertible (A?1 exists).
      Can solve Ax = b as ? = A?1 b.
                          x
      The above solution is unique.
      For homogeneous system Ax = 0, the only solution is x = 0.




Y. Oyamada (Keio Univ. and TUM)   Singular and Non-singular Matrix   April 10, 2012   2/4
Singular




A is singular means that A is not invertible (A?1 doet not exist).
     Either
             a solution to Ax = b does not exist,
             there is more than one solution (not unique).
      The homogeneous system Ax = 0 has more than one solution.
             In?nitely many non-trivial solutions.




Y. Oyamada (Keio Univ. and TUM)   Singular and Non-singular Matrix   April 10, 2012   3/4
Comparison


                            Non-singular                                Singular
 A is                       invertible                                  not invertible
 Columns                    independent                                 dependent
 Rows                       independent                                 dependent
 det(A)                     =0                                          =0
 Ax = 0                     one solution x = 0                          in?nitely many solution
 Ax = b                     one solution                                no solution or in?nitely many
 A has                      n (nonzero) pivots                          r < n pivots
 A has                      full rank r = n                             rank r < n
 Column space               is all of Rn                                has dimension r < n
 Row space                  is all of Rn                                has dimension r < n
 Eigenvalue                 All eigenvalues are non-zero                Zero is an eigenvalue of A
 AT A                       is symmetric positive de?nite               is only semide?nite
 Singular value of A        has n (positive) singular values            has r < n singular values




Y. Oyamada (Keio Univ. and TUM)      Singular and Non-singular Matrix                 April 10, 2012   4/4

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Comparison Singular and Non-singular

  • 1. Singular and Non-singular Matrix Yuji Oyamada 1 HVRL, Keio University 2 Chair for Computer Aided Medical Procedure (CAMP), Technische Universit:t M:nchen a u April 10, 2012
  • 2. Non-Singular A is non-singular means that A is invertible (A?1 exists). Can solve Ax = b as ? = A?1 b. x The above solution is unique. For homogeneous system Ax = 0, the only solution is x = 0. Y. Oyamada (Keio Univ. and TUM) Singular and Non-singular Matrix April 10, 2012 2/4
  • 3. Singular A is singular means that A is not invertible (A?1 doet not exist). Either a solution to Ax = b does not exist, there is more than one solution (not unique). The homogeneous system Ax = 0 has more than one solution. In?nitely many non-trivial solutions. Y. Oyamada (Keio Univ. and TUM) Singular and Non-singular Matrix April 10, 2012 3/4
  • 4. Comparison Non-singular Singular A is invertible not invertible Columns independent dependent Rows independent dependent det(A) =0 =0 Ax = 0 one solution x = 0 in?nitely many solution Ax = b one solution no solution or in?nitely many A has n (nonzero) pivots r < n pivots A has full rank r = n rank r < n Column space is all of Rn has dimension r < n Row space is all of Rn has dimension r < n Eigenvalue All eigenvalues are non-zero Zero is an eigenvalue of A AT A is symmetric positive de?nite is only semide?nite Singular value of A has n (positive) singular values has r < n singular values Y. Oyamada (Keio Univ. and TUM) Singular and Non-singular Matrix April 10, 2012 4/4