# Basic Solutions and Linear Combinations

1. Oct 10, 2007

### lapo3399

Just to clarify these concepts: if a homogeneous system of linear equations with four variables z1, z2, z3, and z4 yields a matrix in reduced row echelon form that defines (as an arbitrary example) the linear equations

z1 = z3 + 0.5z4 = t + 0.5s
z2 = 2z3 - z4 = 2t - s
z3 = t
z4 = s

then the linear combination should be:

$$\left[ \begin{array}{ c } z1 & z2 & z3 & z4 \end{array} \right] = t \left[ \begin{array}{ c } 1 & 2 & 1 & 0 \end{array} \right] + s \left[ \begin{array}{ c } 0.5 & -1 & 0 & 1 \end{array} \right]$$

and the basic solutions are:

$$\left[ \begin{array}{ c } 1 & 2 & 1 & 0 \end{array} \right] , \left[ \begin{array}{ c } 0.5 & -1 & 0 & 1 \end{array} \right]$$

My main problem is understanding exactly what the basic solutions are. I'm not sure whether they're just the direction vectors multiplied by each of the parameters or whether they include the parameters as well. Please clarify this for me.

Thanks.

2. Oct 25, 2007

### walterman

pls i need some one to help me correct my read subroutine in fortran 77.i must have made some errors and i need to be corrected.Thanks
walterman

c**********************************************************
c**********************************************************
implicit double precision (a-h,o-z)
dimension a(n,n),b(n)
charactername*20, form*50
c
write(*,*)
write(*,*) 'Enter configuration file name: '
open(unit=10,file='fname',status='New',iostat=non)
100 continue
if(nsys.eq.5) then
form='(5f10.5)'
else
form='(6f10.5)'
end if
999 write(*,*)
write(*,'(a,i3,a,f16.8)') ' System size : ',nsys,' x',nsys
write(*,*)
write(*,*) 'xmulticient matrix : '
write(20,fmt=form) ((a(i,j), j=1,nsys), i=1,nsys)
write(*,fmt=form) ((a(i,j), j=1,nsys), i=1,nsys)
write(*,*)
write(*,*) 'constant vector: '
write(21,fmt=form) (b(i), i=1,nsys)
write(*,fmt=form) (b(i), i=1,nsys)
write(*,*)

return
end