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LAPACK 3.3.0
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LAPACK 3.3.0
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00001 SUBROUTINE SSBMV(UPLO,N,K,ALPHA,A,LDA,X,INCX,BETA,Y,INCY) 00002 * .. Scalar Arguments .. 00003 REAL ALPHA,BETA 00004 INTEGER INCX,INCY,K,LDA,N 00005 CHARACTER UPLO 00006 * .. 00007 * .. Array Arguments .. 00008 REAL A(LDA,*),X(*),Y(*) 00009 * .. 00010 * 00011 * Purpose 00012 * ======= 00013 * 00014 * SSBMV performs the matrix-vector operation 00015 * 00016 * y := alpha*A*x + beta*y, 00017 * 00018 * where alpha and beta are scalars, x and y are n element vectors and 00019 * A is an n by n symmetric band matrix, with k super-diagonals. 00020 * 00021 * Arguments 00022 * ========== 00023 * 00024 * UPLO - CHARACTER*1. 00025 * On entry, UPLO specifies whether the upper or lower 00026 * triangular part of the band matrix A is being supplied as 00027 * follows: 00028 * 00029 * UPLO = 'U' or 'u' The upper triangular part of A is 00030 * being supplied. 00031 * 00032 * UPLO = 'L' or 'l' The lower triangular part of A is 00033 * being supplied. 00034 * 00035 * Unchanged on exit. 00036 * 00037 * N - INTEGER. 00038 * On entry, N specifies the order of the matrix A. 00039 * N must be at least zero. 00040 * Unchanged on exit. 00041 * 00042 * K - INTEGER. 00043 * On entry, K specifies the number of super-diagonals of the 00044 * matrix A. K must satisfy 0 .le. K. 00045 * Unchanged on exit. 00046 * 00047 * ALPHA - REAL . 00048 * On entry, ALPHA specifies the scalar alpha. 00049 * Unchanged on exit. 00050 * 00051 * A - REAL array of DIMENSION ( LDA, n ). 00052 * Before entry with UPLO = 'U' or 'u', the leading ( k + 1 ) 00053 * by n part of the array A must contain the upper triangular 00054 * band part of the symmetric matrix, supplied column by 00055 * column, with the leading diagonal of the matrix in row 00056 * ( k + 1 ) of the array, the first super-diagonal starting at 00057 * position 2 in row k, and so on. The top left k by k triangle 00058 * of the array A is not referenced. 00059 * The following program segment will transfer the upper 00060 * triangular part of a symmetric band matrix from conventional 00061 * full matrix storage to band storage: 00062 * 00063 * DO 20, J = 1, N 00064 * M = K + 1 - J 00065 * DO 10, I = MAX( 1, J - K ), J 00066 * A( M + I, J ) = matrix( I, J ) 00067 * 10 CONTINUE 00068 * 20 CONTINUE 00069 * 00070 * Before entry with UPLO = 'L' or 'l', the leading ( k + 1 ) 00071 * by n part of the array A must contain the lower triangular 00072 * band part of the symmetric matrix, supplied column by 00073 * column, with the leading diagonal of the matrix in row 1 of 00074 * the array, the first sub-diagonal starting at position 1 in 00075 * row 2, and so on. The bottom right k by k triangle of the 00076 * array A is not referenced. 00077 * The following program segment will transfer the lower 00078 * triangular part of a symmetric band matrix from conventional 00079 * full matrix storage to band storage: 00080 * 00081 * DO 20, J = 1, N 00082 * M = 1 - J 00083 * DO 10, I = J, MIN( N, J + K ) 00084 * A( M + I, J ) = matrix( I, J ) 00085 * 10 CONTINUE 00086 * 20 CONTINUE 00087 * 00088 * Unchanged on exit. 00089 * 00090 * LDA - INTEGER. 00091 * On entry, LDA specifies the first dimension of A as declared 00092 * in the calling (sub) program. LDA must be at least 00093 * ( k + 1 ). 00094 * Unchanged on exit. 00095 * 00096 * X - REAL array of DIMENSION at least 00097 * ( 1 + ( n - 1 )*abs( INCX ) ). 00098 * Before entry, the incremented array X must contain the 00099 * vector x. 00100 * Unchanged on exit. 00101 * 00102 * INCX - INTEGER. 00103 * On entry, INCX specifies the increment for the elements of 00104 * X. INCX must not be zero. 00105 * Unchanged on exit. 00106 * 00107 * BETA - REAL . 00108 * On entry, BETA specifies the scalar beta. 00109 * Unchanged on exit. 00110 * 00111 * Y - REAL array of DIMENSION at least 00112 * ( 1 + ( n - 1 )*abs( INCY ) ). 00113 * Before entry, the incremented array Y must contain the 00114 * vector y. On exit, Y is overwritten by the updated vector y. 00115 * 00116 * INCY - INTEGER. 00117 * On entry, INCY specifies the increment for the elements of 00118 * Y. INCY must not be zero. 00119 * Unchanged on exit. 00120 * 00121 * Further Details 00122 * =============== 00123 * 00124 * Level 2 Blas routine. 00125 * 00126 * -- Written on 22-October-1986. 00127 * Jack Dongarra, Argonne National Lab. 00128 * Jeremy Du Croz, Nag Central Office. 00129 * Sven Hammarling, Nag Central Office. 00130 * Richard Hanson, Sandia National Labs. 00131 * 00132 * ===================================================================== 00133 * 00134 * .. Parameters .. 00135 REAL ONE,ZERO 00136 PARAMETER (ONE=1.0E+0,ZERO=0.0E+0) 00137 * .. 00138 * .. Local Scalars .. 00139 REAL TEMP1,TEMP2 00140 INTEGER I,INFO,IX,IY,J,JX,JY,KPLUS1,KX,KY,L 00141 * .. 00142 * .. External Functions .. 00143 LOGICAL LSAME 00144 EXTERNAL LSAME 00145 * .. 00146 * .. External Subroutines .. 00147 EXTERNAL XERBLA 00148 * .. 00149 * .. Intrinsic Functions .. 00150 INTRINSIC MAX,MIN 00151 * .. 00152 * 00153 * Test the input parameters. 00154 * 00155 INFO = 0 00156 IF (.NOT.LSAME(UPLO,'U') .AND. .NOT.LSAME(UPLO,'L')) THEN 00157 INFO = 1 00158 ELSE IF (N.LT.0) THEN 00159 INFO = 2 00160 ELSE IF (K.LT.0) THEN 00161 INFO = 3 00162 ELSE IF (LDA.LT. (K+1)) THEN 00163 INFO = 6 00164 ELSE IF (INCX.EQ.0) THEN 00165 INFO = 8 00166 ELSE IF (INCY.EQ.0) THEN 00167 INFO = 11 00168 END IF 00169 IF (INFO.NE.0) THEN 00170 CALL XERBLA('SSBMV ',INFO) 00171 RETURN 00172 END IF 00173 * 00174 * Quick return if possible. 00175 * 00176 IF ((N.EQ.0) .OR. ((ALPHA.EQ.ZERO).AND. (BETA.EQ.ONE))) RETURN 00177 * 00178 * Set up the start points in X and Y. 00179 * 00180 IF (INCX.GT.0) THEN 00181 KX = 1 00182 ELSE 00183 KX = 1 - (N-1)*INCX 00184 END IF 00185 IF (INCY.GT.0) THEN 00186 KY = 1 00187 ELSE 00188 KY = 1 - (N-1)*INCY 00189 END IF 00190 * 00191 * Start the operations. In this version the elements of the array A 00192 * are accessed sequentially with one pass through A. 00193 * 00194 * First form y := beta*y. 00195 * 00196 IF (BETA.NE.ONE) THEN 00197 IF (INCY.EQ.1) THEN 00198 IF (BETA.EQ.ZERO) THEN 00199 DO 10 I = 1,N 00200 Y(I) = ZERO 00201 10 CONTINUE 00202 ELSE 00203 DO 20 I = 1,N 00204 Y(I) = BETA*Y(I) 00205 20 CONTINUE 00206 END IF 00207 ELSE 00208 IY = KY 00209 IF (BETA.EQ.ZERO) THEN 00210 DO 30 I = 1,N 00211 Y(IY) = ZERO 00212 IY = IY + INCY 00213 30 CONTINUE 00214 ELSE 00215 DO 40 I = 1,N 00216 Y(IY) = BETA*Y(IY) 00217 IY = IY + INCY 00218 40 CONTINUE 00219 END IF 00220 END IF 00221 END IF 00222 IF (ALPHA.EQ.ZERO) RETURN 00223 IF (LSAME(UPLO,'U')) THEN 00224 * 00225 * Form y when upper triangle of A is stored. 00226 * 00227 KPLUS1 = K + 1 00228 IF ((INCX.EQ.1) .AND. (INCY.EQ.1)) THEN 00229 DO 60 J = 1,N 00230 TEMP1 = ALPHA*X(J) 00231 TEMP2 = ZERO 00232 L = KPLUS1 - J 00233 DO 50 I = MAX(1,J-K),J - 1 00234 Y(I) = Y(I) + TEMP1*A(L+I,J) 00235 TEMP2 = TEMP2 + A(L+I,J)*X(I) 00236 50 CONTINUE 00237 Y(J) = Y(J) + TEMP1*A(KPLUS1,J) + ALPHA*TEMP2 00238 60 CONTINUE 00239 ELSE 00240 JX = KX 00241 JY = KY 00242 DO 80 J = 1,N 00243 TEMP1 = ALPHA*X(JX) 00244 TEMP2 = ZERO 00245 IX = KX 00246 IY = KY 00247 L = KPLUS1 - J 00248 DO 70 I = MAX(1,J-K),J - 1 00249 Y(IY) = Y(IY) + TEMP1*A(L+I,J) 00250 TEMP2 = TEMP2 + A(L+I,J)*X(IX) 00251 IX = IX + INCX 00252 IY = IY + INCY 00253 70 CONTINUE 00254 Y(JY) = Y(JY) + TEMP1*A(KPLUS1,J) + ALPHA*TEMP2 00255 JX = JX + INCX 00256 JY = JY + INCY 00257 IF (J.GT.K) THEN 00258 KX = KX + INCX 00259 KY = KY + INCY 00260 END IF 00261 80 CONTINUE 00262 END IF 00263 ELSE 00264 * 00265 * Form y when lower triangle of A is stored. 00266 * 00267 IF ((INCX.EQ.1) .AND. (INCY.EQ.1)) THEN 00268 DO 100 J = 1,N 00269 TEMP1 = ALPHA*X(J) 00270 TEMP2 = ZERO 00271 Y(J) = Y(J) + TEMP1*A(1,J) 00272 L = 1 - J 00273 DO 90 I = J + 1,MIN(N,J+K) 00274 Y(I) = Y(I) + TEMP1*A(L+I,J) 00275 TEMP2 = TEMP2 + A(L+I,J)*X(I) 00276 90 CONTINUE 00277 Y(J) = Y(J) + ALPHA*TEMP2 00278 100 CONTINUE 00279 ELSE 00280 JX = KX 00281 JY = KY 00282 DO 120 J = 1,N 00283 TEMP1 = ALPHA*X(JX) 00284 TEMP2 = ZERO 00285 Y(JY) = Y(JY) + TEMP1*A(1,J) 00286 L = 1 - J 00287 IX = JX 00288 IY = JY 00289 DO 110 I = J + 1,MIN(N,J+K) 00290 IX = IX + INCX 00291 IY = IY + INCY 00292 Y(IY) = Y(IY) + TEMP1*A(L+I,J) 00293 TEMP2 = TEMP2 + A(L+I,J)*X(IX) 00294 110 CONTINUE 00295 Y(JY) = Y(JY) + ALPHA*TEMP2 00296 JX = JX + INCX 00297 JY = JY + INCY 00298 120 CONTINUE 00299 END IF 00300 END IF 00301 * 00302 RETURN 00303 * 00304 * End of SSBMV . 00305 * 00306 END
1.7.3 
