15c challenge: accuracy of a complex equation system

[Werner]

mh a residual correction step still does not get 9-10 digits correct (nor a second one)

the following program will perform the solve and a residual correction, and allows for subsequent corrections:
You will need to be in big mode to run this program.

In: X:A Y:b
GSB A -> result C of solve + 1 residual correction
GSB C -> perform an additional residual correction

remark that the original matrix A is now in D, should you wish to recover it.

LBL B
STO MATRIX D
RESULT C
/
LBL C
RCL MATRIX B
STO MATRIX E
RESULT E
RCL MATRIX D
RCL MATRIX C
MATRIX 6
RCL MATRIX A
/
RCL MATRIX C
RESULT C
+
RTN

after first step:

1.995794978e-4 4.096399076e-3
-1.448833623e-3 -3.563298309e-2
-1.454083177e-3 -3.563276084e-2
5.344581171e-5 -2.259868262e-6

after GSB C:

1.995795337e-4
-1.448833607e-3
..

element C(2,1) has actually gotten worse, and we're nowhere near 9/10 digits correct.
Cheers, Werner