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NAME SLASY2 - solve for the N1 by N2 matrix X, 1 <= N1,N2 <= 2, in op(TL)*X + ISGN*X*op(TR) = SCALE*B, SYNOPSIS SUBROUTINE SLASY2( LTRANL, LTRANR, ISGN, N1, N2, TL, LDTL, TR, LDTR, B, LDB, SCALE, X, LDX, XNORM, INFO ) LOGICAL LTRANL, LTRANR INTEGER INFO, ISGN, LDB, LDTL, LDTR, LDX, N1, N2 REAL SCALE, XNORM REAL B( LDB, * ), TL( LDTL, * ), TR( LDTR, * ), X( LDX, * ) PURPOSE SLASY2 solves for the N1 by N2 matrix X, 1 <= N1,N2 <= 2, in where TL is N1 by N1, TR is N2 by N2, B is N1 by N2, and ISGN = 1 or -1. op(T) = T or T', where T' denotes the tran- spose of T. ARGUMENTS LTRANL (input) LOGICAL On entry, LTRANL specifies the op(TL): = .FALSE., op(TL) = TL, = .TRUE., op(TL) = TL'. LTRANR (input) LOGICAL On entry, LTRANR specifies the op(TR): = .FALSE., op(TR) = TR, = .TRUE., op(TR) = TR'. ISGN (input) INTEGER On entry, ISGN specifies the sign of the equation as described before. ISGN may only be 1 or -1. N1 (input) INTEGER On entry, N1 specifies the order of matrix TL. N1 may only be 0, 1 or 2. N2 (input) INTEGER On entry, N2 specifies the order of matrix TR. N2 may only be 0, 1 or 2. TL (input) REAL array, dimension (LDTL,2) On entry, TL contains an N1 by N1 matrix. LDTL (input) INTEGER The leading dimension of the matrix TL. LDTL >= max(1,N1). TR (input) REAL array, dimension (LDTR,2) On entry, TR contains an N2 by N2 matrix. LDTR (input) INTEGER The leading dimension of the matrix TR. LDTR >= max(1,N2). B (input) REAL array, dimension (LDB,2) On entry, the N1 by N2 matrix B contains the right- hand side of the equation. LDB (input) INTEGER The leading dimension of the matrix B. LDB >= max(1,N1). SCALE (output) REAL On exit, SCALE contains the scale factor. SCALE is chosen less than or equal to 1 to prevent the solu- tion overflowing. X (output) REAL array, dimension (LDX,2) On exit, X contains the N1 by N2 solution. LDX (input) INTEGER The leading dimension of the matrix X. LDX >= max(1,N1). XNORM (output) REAL On exit, XNORM is the infinity-norm of the solution. INFO (output) INTEGER On exit, INFO is set to 0: successful exit. 1: TL and TR have too close eigenvalues, so TL or TR is perturbed to get a nonsingular equation. NOTE: In the interests of speed, this routine does not check the inputs for errors.