SUBROUTINE CGECO(A,LDA,N,IPVT,RCOND,Z) C***BEGIN PROLOGUE CGECO C***DATE WRITTEN 780814 (YYMMDD) C***REVISION DATE 820801 (YYMMDD) C***CATEGORY NO. D2C1 C***KEYWORDS COMPLEX,CONDITION,FACTOR,LINEAR ALGEBRA,LINPACK,MATRIX C***AUTHOR MOLER, C. B., (U. OF NEW MEXICO) C***PURPOSE Factors a COMPLEX matrix by Gaussian elimination and C estimates the condition of the matrix. C***DESCRIPTION C C CGECO factors a complex matrix by Gaussian elimination C and estimates the condition of the matrix. C C If RCOND is not needed, CGEFA is slightly faster. C To solve A*X = B , follow CGECO By CGESL. C To Compute INVERSE(A)*C , follow CGECO by CGESL. C To compute DETERMINANT(A) , follow CGECO by CGEDI. C To compute INVERSE(A) , follow CGECO by CGEDI. C C On Entry C C A COMPLEX(LDA, N) C the matrix to be factored. 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 On Return C C A an upper triangular matrix and the multipliers C which were used to obtain it. C The factorization can be written A = L*U where C L is a product of permutation and unit lower C triangular matrices and U is upper triangular. C C IPVT INTEGER(N) C an integer vector of pivot indices. C C RCOND REAL C an estimate of the reciprocal condition of A . C For the system A*X = B , relative perturbations C in A and B of size EPSILON may cause C relative perturbations in X of size EPSILON/RCOND . C If RCOND is so small that the logical expression C 1.0 + RCOND .EQ. 1.0 C is true, then A may be singular to working C precision. In particular, RCOND is zero if C exact singularity is detected or the estimate C underflows. C C Z COMPLEX(N) C a work vector whose contents are usually unimportant. C If A is close to a singular matrix, then Z is C an approximate null vector in the sense that C NORM(A*Z) = RCOND*NORM(A)*NORM(Z) . 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 LINPACK CGEFA C BLAS CAXPY,CDOTC,CSSCAL,SCASUM C Fortran ABS,AIMAG,AMAX1,CMPLX,CONJG,REAL C***REFERENCES DONGARRA J.J., BUNCH J.R., MOLER C.B., STEWART G.W., C *LINPACK USERS GUIDE*, SIAM, 1979. C***ROUTINES CALLED CAXPY,CDOTC,CGEFA,CSSCAL,SCASUM C***END PROLOGUE CGECO