[50G] Question

[Tugdual]

(03-28-2015 12:42 PM)Gilles Wrote:  

(03-24-2015 06:41 AM)Tugdual Wrote:  You tickle my curiosity. Do you mean something like building and solving a system of equations by developing LU=A?

yes...

EDIT : this v2 allows parameters in the input matrix

Code:

LU2
«
 DUP SIZE HEAD → d     @ Empile A. Ordre de la matrice : d
 « d DUP
  « → I J 
   « CASE 
     'I==J' THEN 1 END
     'I<J'  THEN 0 END
     "l" I + J + S~N 
     END
   » 
  » LCXM               @ Initialse L

  d DUP
  « → I J 
   « CASE 
    'I>J' THEN 0 END
     "u" I + J + S~N  
     END
   » 
  » LCXM              @ Initialise U
  
  → L U
  «
   L U * LVAR UNROT
   AXL SWAP AXL 2. «=» DOLIST
   «EVAL» DOSUBS AXL  SWAP SOLVE 
   IF DUP {} == THEN DROP "No LU factorisation" DOERR END
   HEAD DUP
   
   L SWAP SUBST        @ renvoie L
   SWAP U SWAP SUBST   @ renvoie U
  » 
 » 
»

The code is from HPUserEdit
Exact mode, and flag -86 set (or 256 ATTACH)
To understand how it works, the debug mode is perfect.

Hi Gilles, thanks for digging this up this from your archives. Very interesting piece of code, the matrices fabrication is pretty tricky showing interesting features of the 50g. Use of Solve is a bit expensive but this is very instructive.