% ax=b implies x= b / a or x = inv(A) b
% x = a \ b ;
% a= [1 2  10 ;  0 5 30 ; 0  0 48]
% a = [ 1 2 4 ;  3 15 60 ; 4 16 64 ]
 c = [ 1 2 3 ; 4 12 36 ; 5 25 125];
 d = c' * c;

 a = d
 b = [ 1; 2; 3]

 x=  a\b
 a*x 
 a*x - b
 a*x == b
 key=input('press y to continue');

 y=  linsolve(a,b)
 a*y
 a*y - b
 a*y == b 

 key=input('press y to continue');
 clear opt
 opt.SYM   =true
 opt.POSDEF=true;
 yy=linsolve(a,b,opt)
 a*yy == b
 a*yy-b == 0

 key=input('press y to continue');

 f=inv(a)
 f*a
 a*f
 a*f == f * a
 a \ eye(3)
