HP 48gII - Manual (Page 369)

Page 11-43
The result is the augmented matrix corresponding to the system of equations:
X+Y = 0
X-Y =2
Residual errors in linear system solutions (Function RSD)
Function RSD calculates the ReSiDuals or errors in the solution of the matrix
equation
A⋅x=b, representing a system of n linear equations in n unknowns.
We can think of solving this system as solving the matrix equation: f( x) = b -
A⋅x = 0. Suppose that, through a numerical method, we produce as a first
approximation the solution
x(0). Evaluating f(x(0)) = b - A⋅x(0) = e ≠ 0.
Thus, e is a vector of residuals of Function for the vector x = x (0).
To use Function RSD you need the terms
b, A, and x(0), as arguments. The
vector returned is e = b - A⋅x(0). For example, using A =
[[2,-1][0,2]], x(0) = [1.8,2.7], and b = [1,6], we can find
the vector of residuals as follows:
The result is
e = b - A⋅x(0) = [ 0.1 0.6 ].
Note: If we let the vector ∆x = x – x (0), represent the correction in the
values of
x (0), we can write a new matrix equation for ∆x, namely A⋅∆x =
e. Solving for ∆x we can find the actual solution of the original system as x
=
x(0) + ∆x.