SUBROUTINE SQRSL(X,LDX,N,K,QRAUX,Y,QY,QTY,B,RSD,XB,JOB,INFO) INTEGER LDX,N,K,JOB,INFO REAL X(LDX,1),QRAUX(1),Y(1),QY(1),QTY(1),B(1),RSD(1),XB(1) C C SQRSL APPLIES THE OUTPUT OF SQRDC TO COMPUTE COORDINATE C TRANSFORMATIONS, PROJECTIONS, AND LEAST SQUARES SOLUTIONS. C FOR K .LE. MIN(N,P), LET XK BE THE MATRIX C C XK = (X(JPVT(1)),X(JPVT(2)), ... ,X(JPVT(K))) C C FORMED FROM COLUMNNS JPVT(1), ... ,JPVT(K) OF THE ORIGINAL C N X P MATRIX X THAT WAS INPUT TO SQRDC (IF NO PIVOTING WAS C DONE, XK CONSISTS OF THE FIRST K COLUMNS OF X IN THEIR C ORIGINAL ORDER). SQRDC PRODUCES A FACTORED ORTHOGONAL MATRIX Q C AND AN UPPER TRIANGULAR MATRIX R SUCH THAT C C XK = Q * (R) C (0) C C THIS INFORMATION IS CONTAINED IN CODED FORM IN THE ARRAYS C X AND QRAUX. C C ON ENTRY C C X REAL(LDX,P). C X CONTAINS THE OUTPUT OF SQRDC. C C LDX INTEGER. C LDX IS THE LEADING DIMENSION OF THE ARRAY X. C C N INTEGER. C N IS THE NUMBER OF ROWS OF THE MATRIX XK. IT MUST C HAVE THE SAME VALUE AS N IN SQRDC. C C K INTEGER. C K IS THE NUMBER OF COLUMNS OF THE MATRIX XK. K C MUST NNOT BE GREATER THAN MIN(N,P), WHERE P IS THE C SAME AS IN THE CALLING SEQUENCE TO SQRDC. C C QRAUX REAL(P). C QRAUX CONTAINS THE AUXILIARY OUTPUT FROM SQRDC. C C Y REAL(N) C Y CONTAINS AN N-VECTOR THAT IS TO BE MANIPULATED C BY SQRSL. C C JOB INTEGER. C JOB SPECIFIES WHAT IS TO BE COMPUTED. JOB HAS C THE DECIMAL EXPANSION ABCDE, WITH THE FOLLOWING C MEANING. C C IF A.NE.0, COMPUTE QY. C IF B,C,D, OR E .NE. 0, COMPUTE QTY. C IF C.NE.0, COMPUTE B. C IF D.NE.0, COMPUTE RSD. C IF E.NE.0, COMPUTE XB. C C NOTE THAT A REQUEST TO COMPUTE B, RSD, OR XB C AUTOMATICALLY TRIGGERS THE COMPUTATION OF QTY, FOR C WHICH AN ARRAY MUST BE PROVIDED IN THE CALLING C SEQUENCE. C C ON RETURN C C QY REAL(N). C QY CONNTAINS Q*Y, IF ITS COMPUTATION HAS BEEN C REQUESTED. C C QTY REAL(N). C QTY CONTAINS TRANS(Q)*Y, IF ITS COMPUTATION HAS C BEEN REQUESTED. HERE TRANS(Q) IS THE C TRANSPOSE OF THE MATRIX Q. C C B REAL(K) C B CONTAINS THE SOLUTION OF THE LEAST SQUARES PROBLEM C C MINIMIZE NORM2(Y - XK*B), C C IF ITS COMPUTATION HAS BEEN REQUESTED. (NOTE THAT C IF PIVOTING WAS REQUESTED IN SQRDC, THE J-TH C COMPONENT OF B WILL BE ASSOCIATED WITH COLUMN JPVT(J) C OF THE ORIGINAL MATRIX X THAT WAS INPUT INTO SQRDC.) C C RSD REAL(N). C RSD CONTAINS THE LEAST SQUARES RESIDUAL Y - XK*B, C IF ITS COMPUTATION HAS BEEN REQUESTED. RSD IS C ALSO THE ORTHOGONAL PROJECTION OF Y ONTO THE C ORTHOGONAL COMPLEMENT OF THE COLUMN SPACE OF XK. C C XB REAL(N). C XB CONTAINS THE LEAST SQUARES APPROXIMATION XK*B, C IF ITS COMPUTATION HAS BEEN REQUESTED. XB IS ALSO C THE ORTHOGONAL PROJECTION OF Y ONTO THE COLUMN SPACE C OF X. C C INFO INTEGER. C INFO IS ZERO UNLESS THE COMPUTATION OF B HAS C BEEN REQUESTED AND R IS EXACTLY SINGULAR. IN C THIS CASE, INFO IS THE INDEX OF THE FIRST ZERO C DIAGONAL ELEMENT OF R AND B IS LEFT UNALTERED. C C THE PARAMETERS QY, QTY, B, RSD, AND XB ARE NOT REFERENCED C IF THEIR COMPUTATION IS NOT REQUESTED AND IN THIS CASE C CAN BE REPLACED BY DUMMY VARIABLES IN THE CALLING PROGRAM. C TO SAVE STORAGE, THE USER MAY IN SOME CASES USE THE SAME C ARRAY FOR DIFFERENT PARAMETERS IN THE CALLING SEQUENCE. A C FREQUENTLY OCCURING EXAMPLE IS WHEN ONE WISHES TO COMPUTE C ANY OF B, RSD, OR XB AND DOES NOT NEED Y OR QTY. IN THIS C CASE ONE MAY IDENTIFY Y, QTY, AND ONE OF B, RSD, OR XB, WHILE C PROVIDING SEPARATE ARRAYS FOR ANYTHING ELSE THAT IS TO BE C COMPUTED. THUS THE CALLING SEQUENCE C C CALL SQRSL(X,LDX,N,K,QRAUX,Y,DUM,Y,B,Y,DUM,110,INFO) C C WILL RESULT IN THE COMPUTATION OF B AND RSD, WITH RSD C OVERWRITING Y. MORE GENERALLY, EACH ITEM IN THE FOLLOWING C LIST CONTAINS GROUPS OF PERMISSIBLE IDENTIFICATIONS FOR C A SINGLE CALLINNG SEQUENCE. C C 1. (Y,QTY,B) (RSD) (XB) (QY) C C 2. (Y,QTY,RSD) (B) (XB) (QY) C C 3. (Y,QTY,XB) (B) (RSD) (QY) C C 4. (Y,QY) (QTY,B) (RSD) (XB) C C 5. (Y,QY) (QTY,RSD) (B) (XB) C C 6. (Y,QY) (QTY,XB) (B) (RSD) C C IN ANY GROUP THE VALUE RETURNED IN THE ARRAY ALLOCATED TO C THE GROUP CORRESPONDS TO THE LAST MEMBER OF THE GROUP. C C LINPACK. THIS VERSION DATED 08/14/78 . C G.W. STEWART, UNIVERSITY OF MARYLAND, ARGONNE NATIONAL LAB. C C SQRSL USES THE FOLLOWING FUNCTIONS AND SUBPROGRAMS. C C BLAS SAXPY,SCOPY,SDOT C FORTRAN ABS,MIN0,MOD C C INTERNAL VARIABLES C INTEGER I,J,JJ,JU,KP1 REAL SDOT,T,TEMP LOGICAL CB,CQY,CQTY,CR,CXB C C C SET INFO FLAG. C INFO = 0 C C DETERMINE WHAT IS TO BE COMPUTED. C CQY = JOB/10000 .NE. 0 CQTY = MOD(JOB,10000) .NE. 0 CB = MOD(JOB,1000)/100 .NE. 0 CR = MOD(JOB,100)/10 .NE. 0 CXB = MOD(JOB,10) .NE. 0 JU = MIN0(K,N-1) C C SPECIAL ACTION WHEN N=1. C IF (JU .NE. 0) GO TO 40 IF (CQY) QY(1) = Y(1) IF (CQTY) QTY(1) = Y(1) IF (CXB) XB(1) = Y(1) IF (.NOT.CB) GO TO 30 IF (X(1,1) .NE. 0.0E0) GO TO 10 INFO = 1 GO TO 20 10 CONTINUE B(1) = Y(1)/X(1,1) 20 CONTINUE 30 CONTINUE IF (CR) RSD(1) = 0.0E0 GO TO 250 40 CONTINUE C C SET UP TO COMPUTE QY OR QTY. C IF (CQY) CALL SCOPY(N,Y,1,QY,1) IF (CQTY) CALL SCOPY(N,Y,1,QTY,1) IF (.NOT.CQY) GO TO 70 C C COMPUTE QY. C DO 60 JJ = 1, JU J = JU - JJ + 1 IF (QRAUX(J) .EQ. 0.0E0) GO TO 50 TEMP = X(J,J) X(J,J) = QRAUX(J) T = -SDOT(N-J+1,X(J,J),1,QY(J),1)/X(J,J) CALL SAXPY(N-J+1,T,X(J,J),1,QY(J),1) X(J,J) = TEMP 50 CONTINUE 60 CONTINUE 70 CONTINUE IF (.NOT.CQTY) GO TO 100 C C COMPUTE TRANS(Q)*Y. C DO 90 J = 1, JU IF (QRAUX(J) .EQ. 0.0E0) GO TO 80 TEMP = X(J,J) X(J,J) = QRAUX(J) T = -SDOT(N-J+1,X(J,J),1,QTY(J),1)/X(J,J) CALL SAXPY(N-J+1,T,X(J,J),1,QTY(J),1) X(J,J) = TEMP 80 CONTINUE 90 CONTINUE 100 CONTINUE C C SET UP TO COMPUTE B, RSD, OR XB. C IF (CB) CALL SCOPY(K,QTY,1,B,1) KP1 = K + 1 IF (CXB) CALL SCOPY(K,QTY,1,XB,1) IF (CR .AND. K .LT. N) CALL SCOPY(N-K,QTY(KP1),1,RSD(KP1),1) IF (.NOT.CXB .OR. KP1 .GT. N) GO TO 120 DO 110 I = KP1, N XB(I) = 0.0E0 110 CONTINUE 120 CONTINUE IF (.NOT.CR) GO TO 140 DO 130 I = 1, K RSD(I) = 0.0E0 130 CONTINUE 140 CONTINUE IF (.NOT.CB) GO TO 190 C C COMPUTE B. C DO 170 JJ = 1, K J = K - JJ + 1 IF (X(J,J) .NE. 0.0E0) GO TO 150 INFO = J C ......EXIT GO TO 180 150 CONTINUE B(J) = B(J)/X(J,J) IF (J .EQ. 1) GO TO 160 T = -B(J) CALL SAXPY(J-1,T,X(1,J),1,B,1) 160 CONTINUE 170 CONTINUE 180 CONTINUE 190 CONTINUE IF (.NOT.CR .AND. .NOT.CXB) GO TO 240 C C COMPUTE RSD OR XB AS REQUIRED. C DO 230 JJ = 1, JU J = JU - JJ + 1 IF (QRAUX(J) .EQ. 0.0E0) GO TO 220 TEMP = X(J,J) X(J,J) = QRAUX(J) IF (.NOT.CR) GO TO 200 T = -SDOT(N-J+1,X(J,J),1,RSD(J),1)/X(J,J) CALL SAXPY(N-J+1,T,X(J,J),1,RSD(J),1) 200 CONTINUE IF (.NOT.CXB) GO TO 210 T = -SDOT(N-J+1,X(J,J),1,XB(J),1)/X(J,J) CALL SAXPY(N-J+1,T,X(J,J),1,XB(J),1) 210 CONTINUE X(J,J) = TEMP 220 CONTINUE 230 CONTINUE 240 CONTINUE 250 CONTINUE RETURN END