org.netlib.lapack
Class Spbsvx

java.lang.Object
  extended by org.netlib.lapack.Spbsvx

public class Spbsvx
extends java.lang.Object

Following is the description from the original
Fortran source.  For each array argument, the Java
version will include an integer offset parameter, so
the arguments may not match the description exactly.
Contact seymour@cs.utk.edu with any questions.

* .. * * Purpose * ======= * * SPBSVX uses the Cholesky factorization A = U**T*U or A = L*L**T to * compute the solution to a real system of linear equations * A * X = B, * where A is an N-by-N symmetric positive definite band matrix and X * and B are N-by-NRHS matrices. * * Error bounds on the solution and a condition estimate are also * provided. * * Description * =========== * * The following steps are performed: * * 1. If FACT = 'E', real scaling factors are computed to equilibrate * the system: * diag(S) * A * diag(S) * inv(diag(S)) * X = diag(S) * B * Whether or not the system will be equilibrated depends on the * scaling of the matrix A, but if equilibration is used, A is * overwritten by diag(S)*A*diag(S) and B by diag(S)*B. * * 2. If FACT = 'N' or 'E', the Cholesky decomposition is used to * factor the matrix A (after equilibration if FACT = 'E') as * A = U**T * U, if UPLO = 'U', or * A = L * L**T, if UPLO = 'L', * where U is an upper triangular band matrix, and L is a lower * triangular band matrix. * * 3. If the leading i-by-i principal minor is not positive definite, * then the routine returns with INFO = i. Otherwise, the factored * form of A is used to estimate the condition number of the matrix * A. If the reciprocal of the condition number is less than machine * precision, INFO = N+1 is returned as a warning, but the routine * still goes on to solve for X and compute error bounds as * described below. * * 4. The system of equations is solved for X using the factored form * of A. * * 5. Iterative refinement is applied to improve the computed solution * matrix and calculate error bounds and backward error estimates * for it. * * 6. If equilibration was used, the matrix X is premultiplied by * diag(S) so that it solves the original system before * equilibration. * * Arguments * ========= * * FACT (input) CHARACTER*1 * Specifies whether or not the factored form of the matrix A is * supplied on entry, and if not, whether the matrix A should be * equilibrated before it is factored. * = 'F': On entry, AFB contains the factored form of A. * If EQUED = 'Y', the matrix A has been equilibrated * with scaling factors given by S. AB and AFB will not * be modified. * = 'N': The matrix A will be copied to AFB and factored. * = 'E': The matrix A will be equilibrated if necessary, then * copied to AFB and factored. * * UPLO (input) CHARACTER*1 * = 'U': Upper triangle of A is stored; * = 'L': Lower triangle of A is stored. * * N (input) INTEGER * The number of linear equations, i.e., the order of the * matrix A. N >= 0. * * KD (input) INTEGER * The number of superdiagonals of the matrix A if UPLO = 'U', * or the number of subdiagonals if UPLO = 'L'. KD >= 0. * * NRHS (input) INTEGER * The number of right-hand sides, i.e., the number of columns * of the matrices B and X. NRHS >= 0. * * AB (input/output) REAL array, dimension (LDAB,N) * On entry, the upper or lower triangle of the symmetric band * matrix A, stored in the first KD+1 rows of the array, except * if FACT = 'F' and EQUED = 'Y', then A must contain the * equilibrated matrix diag(S)*A*diag(S). The j-th column of A * is stored in the j-th column of the array AB as follows: * if UPLO = 'U', AB(KD+1+i-j,j) = A(i,j) for max(1,j-KD)<=i<=j; * if UPLO = 'L', AB(1+i-j,j) = A(i,j) for j<=i<=min(N,j+KD). * See below for further details. * * On exit, if FACT = 'E' and EQUED = 'Y', A is overwritten by * diag(S)*A*diag(S). * * LDAB (input) INTEGER * The leading dimension of the array A. LDAB >= KD+1. * * AFB (input or output) REAL array, dimension (LDAFB,N) * If FACT = 'F', then AFB is an input argument and on entry * contains the triangular factor U or L from the Cholesky * factorization A = U**T*U or A = L*L**T of the band matrix * A, in the same storage format as A (see AB). If EQUED = 'Y', * then AFB is the factored form of the equilibrated matrix A. * * If FACT = 'N', then AFB is an output argument and on exit * returns the triangular factor U or L from the Cholesky * factorization A = U**T*U or A = L*L**T. * * If FACT = 'E', then AFB is an output argument and on exit * returns the triangular factor U or L from the Cholesky * factorization A = U**T*U or A = L*L**T of the equilibrated * matrix A (see the description of A for the form of the * equilibrated matrix). * * LDAFB (input) INTEGER * The leading dimension of the array AFB. LDAFB >= KD+1. * * EQUED (input or output) CHARACTER*1 * Specifies the form of equilibration that was done. * = 'N': No equilibration (always true if FACT = 'N'). * = 'Y': Equilibration was done, i.e., A has been replaced by * diag(S) * A * diag(S). * EQUED is an input argument if FACT = 'F'; otherwise, it is an * output argument. * * S (input or output) REAL array, dimension (N) * The scale factors for A; not accessed if EQUED = 'N'. S is * an input argument if FACT = 'F'; otherwise, S is an output * argument. If FACT = 'F' and EQUED = 'Y', each element of S * must be positive. * * B (input/output) REAL array, dimension (LDB,NRHS) * On entry, the N-by-NRHS right hand side matrix B. * On exit, if EQUED = 'N', B is not modified; if EQUED = 'Y', * B is overwritten by diag(S) * B. * * LDB (input) INTEGER * The leading dimension of the array B. LDB >= max(1,N). * * X (output) REAL array, dimension (LDX,NRHS) * If INFO = 0 or INFO = N+1, the N-by-NRHS solution matrix X to * the original system of equations. Note that if EQUED = 'Y', * A and B are modified on exit, and the solution to the * equilibrated system is inv(diag(S))*X. * * LDX (input) INTEGER * The leading dimension of the array X. LDX >= max(1,N). * * RCOND (output) REAL * The estimate of the reciprocal condition number of the matrix * A after equilibration (if done). If RCOND is less than the * machine precision (in particular, if RCOND = 0), the matrix * is singular to working precision. This condition is * indicated by a return code of INFO > 0. * * FERR (output) REAL array, dimension (NRHS) * The estimated forward error bound for each solution vector * X(j) (the j-th column of the solution matrix X). * If XTRUE is the true solution corresponding to X(j), FERR(j) * is an estimated upper bound for the magnitude of the largest * element in (X(j) - XTRUE) divided by the magnitude of the * largest element in X(j). The estimate is as reliable as * the estimate for RCOND, and is almost always a slight * overestimate of the true error. * * BERR (output) REAL array, dimension (NRHS) * The componentwise relative backward error of each solution * vector X(j) (i.e., the smallest relative change in * any element of A or B that makes X(j) an exact solution). * * WORK (workspace) REAL array, dimension (3*N) * * IWORK (workspace) INTEGER array, dimension (N) * * INFO (output) INTEGER * = 0: successful exit * < 0: if INFO = -i, the i-th argument had an illegal value * > 0: if INFO = i, and i is * <= N: the leading minor of order i of A is * not positive definite, so the factorization * could not be completed, and the solution has not * been computed. RCOND = 0 is returned. * = N+1: U is nonsingular, but RCOND is less than machine * precision, meaning that the matrix is singular * to working precision. Nevertheless, the * solution and error bounds are computed because * there are a number of situations where the * computed solution can be more accurate than the * value of RCOND would suggest. * * Further Details * =============== * * The band storage scheme is illustrated by the following example, when * N = 6, KD = 2, and UPLO = 'U': * * Two-dimensional storage of the symmetric matrix A: * * a11 a12 a13 * a22 a23 a24 * a33 a34 a35 * a44 a45 a46 * a55 a56 * (aij=conjg(aji)) a66 * * Band storage of the upper triangle of A: * * * * a13 a24 a35 a46 * * a12 a23 a34 a45 a56 * a11 a22 a33 a44 a55 a66 * * Similarly, if UPLO = 'L' the format of A is as follows: * * a11 a22 a33 a44 a55 a66 * a21 a32 a43 a54 a65 * * a31 a42 a53 a64 * * * * Array elements marked * are not used by the routine. * * ===================================================================== * * .. Parameters ..


Constructor Summary
Spbsvx()
           
 
Method Summary
static void spbsvx(java.lang.String fact, java.lang.String uplo, int n, int kd, int nrhs, float[] ab, int _ab_offset, int ldab, float[] afb, int _afb_offset, int ldafb, StringW equed, float[] s, int _s_offset, float[] b, int _b_offset, int ldb, float[] x, int _x_offset, int ldx, floatW rcond, float[] ferr, int _ferr_offset, float[] berr, int _berr_offset, float[] work, int _work_offset, int[] iwork, int _iwork_offset, intW info)
           
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

Spbsvx

public Spbsvx()
Method Detail

spbsvx

public static void spbsvx(java.lang.String fact,
                          java.lang.String uplo,
                          int n,
                          int kd,
                          int nrhs,
                          float[] ab,
                          int _ab_offset,
                          int ldab,
                          float[] afb,
                          int _afb_offset,
                          int ldafb,
                          StringW equed,
                          float[] s,
                          int _s_offset,
                          float[] b,
                          int _b_offset,
                          int ldb,
                          float[] x,
                          int _x_offset,
                          int ldx,
                          floatW rcond,
                          float[] ferr,
                          int _ferr_offset,
                          float[] berr,
                          int _berr_offset,
                          float[] work,
                          int _work_offset,
                          int[] iwork,
                          int _iwork_offset,
                          intW info)