-->A=[1 2; 3 4; 5 6]
 A  =
    1.    2.  
    3.    4.  
    5.    6.  
-->[U, S, V] = svd(A)
 V  =
  - 0.6196295  - 0.7848945  
  - 0.7848945    0.6196295  
 S  =
    9.5255181    0.         
    0.           0.5143006  
    0.           0.         
 U  =
  - 0.2298477    0.8834610    0.4082483  
  - 0.5247448    0.2407825  - 0.8164966  
  - 0.8196419  - 0.4018960    0.4082483  
-->U*S*V'
 ans  =
    1.    2.  
    3.    4.  
    5.    6.  
-->[X, D]=spec(A'*A)
 D  =
    0.2645051    0.         
    0.           90.735495  
 X  =
  - 0.7848945    0.6196295  
    0.6196295    0.7848945  
-->S
 S  =
    9.5255181    0.         
    0.           0.5143006  
    0.           0.         
-->sqrt(D)
 ans  =
    0.5143006    0.         
    0.           9.5255181  
-->S.^2
 ans  =
    90.735495    0.         
    0.           0.2645051  
    0.           0.         
-->D
 D  =
    0.2645051    0.         
    0.           90.735495  
-->U(:,1)*S(1,1)*V(:,1)'
 ans  =
    1.3566282    1.7184624  
    3.0971971    3.9232684  
    4.837766     6.1280745  
-->A
 A  =
    1.    2.  
    3.    4.  
    5.    6.  
-->U(:,1)*S(1,1)*V(:,1)' + U(:,2)*S(2,2)*V(:,2)'
 ans  =
    1.    2.  
    3.    4.  
    5.    6.  
--> U(:,2)*S(2,2)*V(:,2)'
 ans  =
  - 0.3566282    0.2815376  
  - 0.0971971    0.0767316  
    0.1622340  - 0.1280745  
-->norm(ans)
 ans  =
    0.5143006  
-->U(:,1)*S(1,1)*V(:,1)'
 ans  =
    1.3566282    1.7184624  
    3.0971971    3.9232684  
    4.837766     6.1280745  
-->norm(ans)
 ans  =
    9.5255181  
-->norm(A)
 ans  =
    9.5255181