Previous: sgefa Up: ../linpack.html Next: sgtsl
SUBROUTINE SGESL(A,LDA,N,IPVT,B,JOB) INTEGER LDA,N,IPVT(1),JOB REAL A(LDA,1),B(1) C C SGESL SOLVES THE REAL SYSTEM C A * X = B OR TRANS(A) * X = B C USING THE FACTORS COMPUTED BY SGECO OR SGEFA. C C ON ENTRY C C A REAL(LDA, N) C THE OUTPUT FROM SGECO OR SGEFA. C C LDA INTEGER C THE LEADING DIMENSION OF THE ARRAY A . C C N INTEGER C THE ORDER OF THE MATRIX A . C C IPVT INTEGER(N) C THE PIVOT VECTOR FROM SGECO OR SGEFA. C C B REAL(N) C THE RIGHT HAND SIDE VECTOR. C C JOB INTEGER C = 0 TO SOLVE A*X = B , C = NONZERO TO SOLVE TRANS(A)*X = B WHERE C TRANS(A) IS THE TRANSPOSE. C C ON RETURN C C B THE SOLUTION VECTOR X . C C ERROR CONDITION C C A DIVISION BY ZERO WILL OCCUR IF THE INPUT FACTOR CONTAINS A C ZERO ON THE DIAGONAL. TECHNICALLY THIS INDICATES SINGULARIT C BUT IT IS OFTEN CAUSED BY IMPROPER ARGUMENTS OR IMPROPER C SETTING OF LDA . IT WILL NOT OCCUR IF THE SUBROUTINES ARE C CALLED CORRECTLY AND IF SGECO HAS SET RCOND .GT. 0.0 C OR SGEFA HAS SET INFO .EQ. 0 . C C TO COMPUTE INVERSE(A) * C WHERE C IS A MATRIX C WITH P COLUMNS C CALL SGECO(A,LDA,N,IPVT,RCOND,Z) C IF (RCOND IS TOO SMALL) GO TO ... C DO 10 J = 1, P C CALL SGESL(A,LDA,N,IPVT,C(1,J),0) C 10 CONTINUE C C LINPACK. THIS VERSION DATED 08/14/78 . C CLEVE MOLER, UNIVERSITY OF NEW MEXICO, ARGONNE NATIONAL LAB. C C SUBROUTINES AND FUNCTIONS C C BLAS SAXPY,SDOT C